My observations:
[A] <2016:
Pilots coming to the regionals had professional experience outside 121, and flew with senior CAs.
[B] 2016-2020:
Pilots coming to the regionals were largely longer-term flight instructors, but flew exclusively with senior CAs from batch A.
[C] 2020-2023:
Pilots coming to the regionals were a mix of ATP fast track types and longer-term instructors, who flew with a mix of CAs from batches A and B.
[D] 2023:
Pilots coming to the regionals are often ATP fast track types or low-time instructors, and they've flown mostly with B and C
[E] >= 2024:
Pilots coming to the regionals are almost solely ATP fast track types or low-time instructors, and they've flown almost exclusively with C and D.
Batches C and D have been forced to upgrade from the left seat to the right seat right at 975 hours (or whatever the minimum is). Training and standards, at my shop, have kept the standards in a decent place, but students increasingly rely on gouge and sheppard air. Batches D and E, I'm seeing a lot of folks who are lacking what I would consider to be basic systems knowledge, or integration of that knowledge. A lot of the ancillary knowledge like meteorology, aviation physiology, and aerodynamics seem to be less understood than in times past.
IFR knowledge, understanding of TERPS criteria, minima and how they apply are also a bit lacking. I'm surprised how many times we get "Maintain 280 or greater" when we're doing 300 and the FO reaches up to slow us down to 280. Every speed reduction we get, I feel like the latest crop will go full boards. On the STAR and the airplane is 290 eight miles from a fix to cross at 280? Full boards.
Overall, though—with a few notable exceptions—they're still performing to standard. At least on my equipment, climb/climb via/descend/descend via (in the US) is well understood. However, with each "generation" from the above, a lot of cultural knowledge is lost, and a lot of the "why." Technique is increasingly trained as procedure, and I get the "TL;DR" vibe when I mention things deeper in manuals.
Who knows what the future holds.
(edited: Apparently xenforo got real confused that I had [ b ] bolded