Sounds good but who is going to fly them or fix them?
The advantage of bigger planes is you can move more people with fewer workers, the supply of Pilots and mechanics is plummetting. RJs fed off the fact that there were a lot of people willing to work for the crap wages they offered as a means to get to the majors, well now most of the majors suck, so why would anyomne want to invest in a carreer and put in what amounts to internships at commuters?
For the most part, these larger RJs are to replace the 37-50 seaters, not just at AA but at the other majors as well. Sure, bigger planes fly more people at lower per seat cost, but they generally have higher per-trip costs, so if you don't fill most of the seats of the bigger plane, it ends up being more expensive than the smaller, lighter plane.
AA wasn't chomping at the bit to get a pilot scope clause (and TWU scope clause) allowing 300 or so 76-seaters so that it could stop flying 737s; it went to war with the pilots and other employees so that it could replace a lot of the 37-50 seaters with 76-seaters. As you point out, larger planes can move people more efficiently, and 76 seaters are a lot larger than 37-44 seaters. The overall size of the AA regional fleet probably won't grow by much, but more of it will have 76 seats and the 37 and 44 seat planes will become beer cans. Even a bunch of the 50 seaters will be grounded.
Who will fly them and who will fix them? Cyborgs, of course.
When there aren't enough pilots and mechanics, then airlines will offer higher pay, which will eventually coerce young people to become pilots and mechanics.
Most of the legacy airlines had essentially a 10 year hiring freeze on new pilots and mechanics. Sure, there were a few exceptions, but with stagnant pay and no new jobs, it's no surprise that fewer kids became pilots mechanics over the past decade. Now that the glut of pilots and mechanics is disappearing, I expect that the companies that want to hire them will offer higher pay.
In the old days, nurses didn't make as much as they do now - and the high demand for nurses is well-known to most people who have been paying attention (including you). Eventually, airlines will offer high enough pay to attract new employees. That's the way the world works.