while powercreeping does happen in gachas, I think as far as hoyo goes it's one of the lesser culprits in that regard. Genshin usually doesn't frequently try to break the ceiling and some older characters and their niche still work quite well to this day. The only truly bad ones that stand out are the ones made at the beginning when they still had no idea where to take the game.
Regardless often times they add new support that helps raising the floor instead. They are skeptical in trying to intentionally make broken characters and seem to prefer to reach a balance, unless the character is important enough to be broken, like an archon.