Advance warning for wall of text, but have an interesting outcome to report following my question in post #122 above.
Yesterday I decided to go ahead and book the more expensive fare on Amex Travel anyway and make use of the $450 card credit.
Once finished, there was a message on the screen that my booking could not be displayed and to contact Chat for details. (Which was weird as I could see the booking). Thought I should contact them anyway to be sure.
The chat person confirmed that everything was ok with the booking & probably a system bug. Asked if he could help with anything else, so I thought why not! I asked him what is the benefit of booking via Amex if the fares are so much more expensive than can be found on QF, particularly given they are the same fare basis code. I explained the only reason I made this particular booking was to use my card's travel credit.
His response was that this has been happening a lot post Covid with a number of airlines. Amex is trying to work on getting prices back in line with the airlines but no luck so far. He then said he would try to reprice the booking to see if he could get the price closer to QF's. Unfortunately he couldn't reduce the price, but here is where it got interesting. Actual chat below:
I'll admit I was sceptical but decided to go ahead so long as he sent me a copy of the chat transcript in case I had to follow up later. Of course he warned me that if I cancelled there was no guarantee that I would be able to get the same fare back on Amex or the fare I was looking at on QF.
Now imagine my surprise this morning to see that the $450 credit has already been applied on my statement!
My guess is this fare difference issue must be generating a lot of flack from card members and Amex are doing what they can to keep customers happy by having this backend process in place.
If anyone else wanted to try this, I'm assuming you still need to make the booking with Amex, then get them on the line (chat probably best) and ask why the fare is higher than QF's. I would be prepared to have proof of the fare difference and from the chat above I imagine the difference would need to be greater than $100.
YMMV and Caveat Emptor and all that, but thought I would share one data point that might be useful to others.