The issue of needing assistance is quite a big factor in my travel. I have needed some form of assistance for over 15 years. For the first few years, I was reluctant to ask for help and was unaware of the options, so I used my cane, went slowly, and felt lucky when the golf buggy offered me a lift for any distance. I didn't consider myself disabled and for many of those years, had not applied for a disabled parking sticker (which I only did at my doctor's suggestion).
However, I also had a lot of accidents and falls at airports, and so I started putting requests for assistance on my bookings. Depending on the airline and its policies, this had mixed outcomes. I would say I most consistently received assistance in the USA; in China it was almost never provided despite the request, and in Europe and Australia about 50-60% of the time. I have often waited between 20 and 60 minutes after landing for a wheelchair or my walking frame to arrive, and quite a few times I waited, only to be told it was too late, the commissionaires had finished for the evening, and I would have to manage without help. (This happened one night, on DJ, when we had arrived at the furthest gate in T2 Sydney, a long walk for me to the luggage carousel). For example, on Thursday, arriving in Adelaide, it took 55 minutes from landing to my being able to get to the taxis (long story, but for another day).
I began travelling with my own walking frame because it gave me a measure of independence in getting to the plane - I did not have to rely on a wheelchair attendant who may be heavily in demand. I can relate to what Jock28 describes for his mother, as I have checked in for an international flight, 3 hours before, and waited so long at the check in (well over 2 hours, and never even getting to the lounge) and then being so late that I heard my name being called as the last passenger to board the flight. When first taking my walking frame, many check in agents refused to let me take it to the airbridge until I insisted they call a supervisor as I knew it could be done. If I were not such a frequent traveller (my walking frame is also WP on QF and DJ), I would probably have accepted their refusal as if it were the rule.
In my experience, the airlines' policy is that wheelchair pax board first and disembark last. As I am always an aisle seat, I get up and get my cane and cabin bag and move forward to wait in the front row of J (and yes, sometimes wishing I had been there all flight!) so as to let the other pax in my row disembark. I am quite conscious that I am more able-bodied than many wheelchair pax for whom this is not an option until the aisle-chair arrives for them, often a wait of 10-20 minutes. If my walking frame is brought quickly to the plane door, I can disembark along with the other pax, but this is not common.
I agree with those on this board who deplore scammers or people claiming assistance when they have no real need. It would be an appalling outcome if scammers resulted in depriving those in genuine need of proper assistance. I have worked enough in the field of disability to know that not all impairments are visible, and am slow to judge people's level of need by merely looking at them. It is not easy to know exactly how to ensure appropriate support is provided to those needing it, without seeming to put people through the wringer. I used to carry a letter from my doctor about setting off metal detectors and needing an aisle seat, and could certainly have a letter setting out the things I can and can't do in terms of stairs, walking distances, standing long periods etc. My mobility parking permit also has my photo, so that is another option to support a request for assistance which cannot be scammed.
In terms of the OP's issue, I don't see why he should have been moved, especially from row 23 with its fixed armrests, unless the nature of the person's disability (leg in a full cast?) required a front row (but obviously not an exit row). Even then there were other vacant seats in that row. I must say that as walking distances is a problem for me, I always aim for a seat near the front (which as a WP I usually am able to get), but as I said above, it is no advantage for a quick disembarkation as you have to wait until last.
As drron said, this issue is only going to increase with an ageing population, many of whom travel more extensively than previous generations. I have seen improvements in airlines asking more questions to determine specific types of assistance which are needed (eg: lifts and hoists to avoid stairs, buggy or wheelchair for walking long distances) although there is some way to go in terms of staff understanding what these mean for the passenger. One advantage of being boarded early, in a wheelchair or using my frame, is that there is a quiet moment to speak to the CSM about what is needed on arrival. Most CSMs have been excellent in this regard. I have had more difficulty with check-in staff understanding my requirements.
Somewhat off-topic, in relation to scams at Disneyland, while I hate the idea of scammers rorting the system and spoiling it for those in need, I have to say that Disney is one of the best providers of appropriate assistance. My biggest problem at Disney is the other park-goers who walk into my chair, sit on me (yes, literally), push in constantly in front of me, and I feel quite invisible. If it weren't for the Disney staff and their helpful attitude, I would have long since given up what is in fact a very pleasurable place to spend a few days. [ /end off-topic rant].
However, I also had a lot of accidents and falls at airports, and so I started putting requests for assistance on my bookings. Depending on the airline and its policies, this had mixed outcomes. I would say I most consistently received assistance in the USA; in China it was almost never provided despite the request, and in Europe and Australia about 50-60% of the time. I have often waited between 20 and 60 minutes after landing for a wheelchair or my walking frame to arrive, and quite a few times I waited, only to be told it was too late, the commissionaires had finished for the evening, and I would have to manage without help. (This happened one night, on DJ, when we had arrived at the furthest gate in T2 Sydney, a long walk for me to the luggage carousel). For example, on Thursday, arriving in Adelaide, it took 55 minutes from landing to my being able to get to the taxis (long story, but for another day).
I began travelling with my own walking frame because it gave me a measure of independence in getting to the plane - I did not have to rely on a wheelchair attendant who may be heavily in demand. I can relate to what Jock28 describes for his mother, as I have checked in for an international flight, 3 hours before, and waited so long at the check in (well over 2 hours, and never even getting to the lounge) and then being so late that I heard my name being called as the last passenger to board the flight. When first taking my walking frame, many check in agents refused to let me take it to the airbridge until I insisted they call a supervisor as I knew it could be done. If I were not such a frequent traveller (my walking frame is also WP on QF and DJ), I would probably have accepted their refusal as if it were the rule.
In my experience, the airlines' policy is that wheelchair pax board first and disembark last. As I am always an aisle seat, I get up and get my cane and cabin bag and move forward to wait in the front row of J (and yes, sometimes wishing I had been there all flight!) so as to let the other pax in my row disembark. I am quite conscious that I am more able-bodied than many wheelchair pax for whom this is not an option until the aisle-chair arrives for them, often a wait of 10-20 minutes. If my walking frame is brought quickly to the plane door, I can disembark along with the other pax, but this is not common.
I agree with those on this board who deplore scammers or people claiming assistance when they have no real need. It would be an appalling outcome if scammers resulted in depriving those in genuine need of proper assistance. I have worked enough in the field of disability to know that not all impairments are visible, and am slow to judge people's level of need by merely looking at them. It is not easy to know exactly how to ensure appropriate support is provided to those needing it, without seeming to put people through the wringer. I used to carry a letter from my doctor about setting off metal detectors and needing an aisle seat, and could certainly have a letter setting out the things I can and can't do in terms of stairs, walking distances, standing long periods etc. My mobility parking permit also has my photo, so that is another option to support a request for assistance which cannot be scammed.
In terms of the OP's issue, I don't see why he should have been moved, especially from row 23 with its fixed armrests, unless the nature of the person's disability (leg in a full cast?) required a front row (but obviously not an exit row). Even then there were other vacant seats in that row. I must say that as walking distances is a problem for me, I always aim for a seat near the front (which as a WP I usually am able to get), but as I said above, it is no advantage for a quick disembarkation as you have to wait until last.
As drron said, this issue is only going to increase with an ageing population, many of whom travel more extensively than previous generations. I have seen improvements in airlines asking more questions to determine specific types of assistance which are needed (eg: lifts and hoists to avoid stairs, buggy or wheelchair for walking long distances) although there is some way to go in terms of staff understanding what these mean for the passenger. One advantage of being boarded early, in a wheelchair or using my frame, is that there is a quiet moment to speak to the CSM about what is needed on arrival. Most CSMs have been excellent in this regard. I have had more difficulty with check-in staff understanding my requirements.
Somewhat off-topic, in relation to scams at Disneyland, while I hate the idea of scammers rorting the system and spoiling it for those in need, I have to say that Disney is one of the best providers of appropriate assistance. My biggest problem at Disney is the other park-goers who walk into my chair, sit on me (yes, literally), push in constantly in front of me, and I feel quite invisible. If it weren't for the Disney staff and their helpful attitude, I would have long since given up what is in fact a very pleasurable place to spend a few days. [ /end off-topic rant].