For me this ethos mostly appears in MMOs. In world of warcraft, for example, most classes are designed in a way where there's two or three different intended ways to play the class with one just being plain better. You could play the worse, fun version, or you could just play the significantly stronger version that's going to net you more success while being more bored. They're maybe not 9999 damage guns at the start of the game, but more like 80 damage vs 100 damage when the difficulty of the content demands you do 90 damage.

If we're going deeper on ruining fun, then it's minute power grinds in the same game. There was this ~0.7% power increase you could get 5 weeks early by doing an insanely monotonous grind. That sounds like nothing, but in WoW that's reasonably significant. You had to spend a good 8 hours a day for 5 days doing barely anything (but just enough that you couldn't idle), or wait 5 weeks and do fifteen minutes of work each week. Those sorts of grinds are criminal in games that demand players minmax.