He's right.
Travellers have long voted with their wallets, and many, though not all, want lower pricing. It's why MRTC at AA didn't work, and it's why Spirit, Allegiant, Frontier, easyjet, Ryanair, Air Asia, etc. can thrive. It's also why E+, Comfort+, etc. can work (even why E+ worked at the same time AAs experiment didn't - it was some of the plane, not all of it) - those who choose to spend more for more legroom can, if can be offered as a perk to FFs, as well, but those who want low-cost tickets can get those, too. Also why the low-end basic fares in Y now work - if you want the lowest price, you can now get it. You just won't get everything else that comes with other Y fares.
If I had to guess, when AAs less legroom rows in the back of economy have a critical mass, they will be blocked for their basic economy equivalent fares, and competitors like UA will do the same thing - reconfigure similarly and hold these less-legroom seats for those on BE fares - doesn't mean BE will be guaranteed it, but a good chance they will get it. It makes sense - you don't want to have people paying regular fares - especially last minute buyers that are doing YBME kind of fares, getting the back set of less legroom seats, and if someone is paying less, they don't really have a reason to complain about getting the least desirable seats in the aircraft. Just what I think.