I just don't think that's true. I regularly travel with colleagues and have issues getting them a seat next to me due to the platinum seat hold unless I do it at a counter. I will be genuinely pissed off if the platinum seat hold is abandoned. If they're on a different ticket, a junior colleague can't select the seat next to me. I've also had the same experience as
@aus_flyer changing seats based on Expert Flyer availability. The examples of kids and colleagues are both instances where airport service from an actual person is absolutely vital.
I'm also surprised by the comments where people say they don't use the service desks. I am 34 and use the app extensively. I still use service desks all the time. Examples are: (1) I regularly check for (and move to) earlier flights which were not offered on app or at the kiosk; (2) I often have to re-route on trips (e.g. cancelling out of a MEL-SYD return leg to go directly to BNE); (3) I reckon on at least half a dozen occasions I've had flights cancelled at the airport due to crosswinds and reduced runways, where I have been rebooked onto something the next day or 8 hours later but have been able to recover the trip because of assistance from lounge staff; (4) on a couple of occasions someone else has booked my flight for me and stuffed up my name, which I've had to fix at the airport; (5) I often check to see if there is a spare seat next to me and move seats if there is one elsewhere just before (or during) boarding after the seats are locked up in the app; (6) I've had success on a couple of occasions getting someone moved onto my flight to prevent the hassle of me having to wait for 30 minutes or an hour at the other end of the SYD-MEL pairing for a colleague to arrive.
If you're someone who travels regularly (ie you are a customer who actually contributes serious revenue to the airline) the service is invaluable. This change is utter lunacy. It's almost as though this move is targeted at people who handover fistfuls of cash to the airline. At the very least they should retain service desks in the Business Lounge.