“Things that are actually working” is a key phrase here.
Don’t nerf anything that’s the correct power level for where you want it, obviously. Just buff the stuff that falls below that power level up to that level.
However, it’s important to remember that sometimes stuff gets released (whether by mistake, malice or incompetence) that is considerably above the desired power level. That might be because it’s interacting with something else in an unexpected way or it just isn’t correctly matching the power level needed. Either way, buffing everything else to the same level would require making everything more powerful than the required power level, which then means you would have to raise the power level requirements, by buffing everything else in the game to match, which is often unworkable. If it’s doable, great, but if not then it’s best just to communicate that honestly and nerf where needed.
Basically, if you have one nail standing up out of a board, you don’t lift the other nails and the board itself, you hammer the nail down to meet the board.
The bigger problem is when you have someone constantly adding new nails that stand way above the board, and refuse to hammer them to the correct level, while they drive in others way too much so they sink into the board and vanish. Balance matters.