i dno about overpowered. leveling up doesnt increase the damage you do. it only gives you skill points and a marginal HP boost. i dont see how skill points make you OP either. silent sprinting is nice, for instance, but does it really break the game during battles? nah
i really dont feel like i've gone overboard with side content either ... often times in games i'll exhaust all side content currently available before moving on with the main quest, until more side stuff becomes available, and rinse repeat. i always found it to be stupid to complete the game, have the story wrap up, and then still do side missions after the fact. i like the conclusion of the story also being the conclusion of the game. stronger effect. but right now i still have what seems like 10-15 side quests and errands in my queue that i haven't gotten to.
as far as what i've done? aside from a healthy amount of side quests, i did all the corrupted zones in the starting area, i've done 3 of the 4 cauldrons, i got blazing suns on all the hunting trials, ive accessed all but one tallneck (not including the Frozen Wilds area... i'm leaving that for a bit later). i also generally kill that i encounter along the way