Performance is subjective. What is acceptable to one person might not be to another.

A game breaking bug might not be considered game breaking by everyone.

No, these are objective. If your game doesn't let you progress and you can't progress any more because something you did fifty hours ago in the game caused it? (Skyrim has some of these) Yeah, that's objective. If performance causes the game to stutter, freeze, and run under 15 FPS for long periods of time, that's objectively bad performance. The idea that someone could just ignore these and play the game anyway doesn't mean they aren't objective problems with the game. It's akin to saying that a bridge being broken isn't an objective problem because people could just swim across the river.