Pretty sure lowering tackle effects player pursuit and consequently pass rush as well. That's the whole "deck of cards" thing everyone (particularly King) always refers to. You're on default AP which plays reasonably well but not perfect. You change just one slider in tackle and all of a sudden it's not just "not enough broken tackles" you're dealing with, it's pass rushers not getting home, which leads to higher completion %, which leads to perceived robo QB, etc.
I'd sooner look at the facemask penalty slider and see if that does anything to the tackle animations. Josh previously eluded to the auto subs potentially effecting gameplay, which is just ridiculous. But if that's the case, I wonder if messing around with RB in/out would have an effect on how hard RB's run. Likewise LB in/out and maybe missed tackles. I don't know. Amping the fatigue up some could have defenders playing tired and colored yellow/orange, which could also lead to more missed tackles, particularly if you're keeping your RB fresh and running while colored green.
Literally grasping at straws here, lol.