Yeah, I mean you picked them for certain roles and their skills haven't changed. Some may not be a good fit for the league (facing too many righties, too many HR parks etc) but there is only so much you can do. If guys are genuinely performing better (looking at OAV, BB and HR) then you can swap them into "A" roles - setup A, closer A - while demoting guys who are genuinely performing bad into "B" roles. And you should obviously check their PC settings so they aren't exceeding their IP/G and running into in-game fatigue.
If you have a lot of extra innings you could also raise their auto-rest. I typically put my RPs at 80, but if they throw every game at 80 they won't do as well as they could, so if they're never recovering you may need to let them rest longer.