You could manually save sliders to use for all players and then set those sliders for every player in the Player Training screen but that's
A) Insanely time-consuming and
B) Not addressing the progression issue in the offseason, which still inflates the open 3pt rating
I'm going to second the OP's post with gusto and it's completely in line with the results I'm getting on my end.
That said ... damn. I was genuinely hoping this wasn't looking as bad as it seemed. I've been hunting for a combination of sliders that stymies this, but there doesn't seem to be a setting we can affect that permanently stops this; all we can do is delay it with the sliders.
I continue to believe the main culprit is the AI progression engine. I can deal with the roster logic, that's been an issue in every franchise mode in history, but the offseason progression has never been this skewed. From what I'm seeing the progression engine is way overvaluing and rewarding the open 3pt shot and not focusing on other aspects of the NBA; the two-way stars, the elite rim protectors, the guys who live on defense (Tony Allen types), etc.
Lowering the effects of progression and in-season training only delays the inevitable and still leads to an unbalanced league, one with a lack of stars and rookies not hitting their true potentials. The lack of rookie progression at or near the default level of 50 is still an issue, but bumping that up will make the open 3pt rating issue worse
This needs to be tuned by the devs on the backend. If they can do it with player contracts, I hope they can do it here. I don't see any other solutions at this point for those of us who want to try to take their league as far as possible.