I think you're right about the MyGM part. They ruined it in 2K20 and my understanding is that now the role-playing elements are no longer in MyNBA (judging purely from complaints I've seen on this board).
I would say that if MyGM is significantly more fun for you than the MyLeague experience, then you may genuinely just be best hanging back on 2K19. If the MyLeague experience is plenty entertaining for you, then there's no reason not to upgrade. You now have more control over the structure / mechanics of your league, including new possibilities afforded by Eras. That's on top of the genuine advances in graphics and gameplay.
The two ideal upgrade options would be:
- 2K24 on PS5/XSX (if the latest gameplay & graphical advances are more important to you than having the most league/Eras functionality and the most realism, i.e., in terms of player models, arenas, scoreboards, etc.)
- 2K23 on PC (if it's vice versa for you, i.e., you value greater functionality + realism > latest graphics + gameplay)
Obviously your access to console vs. PC would likely influence that decision too.