I don't think I know of a woman in Gen X or younger who hasn't reached this point to some degree. It's not about being "mediocre" but about no longer going above and beyond and being completely unappreciated for it.
I gradually stopped doing little things for my husband like buying his snacks at the store or making sure the drinks he liked were in the fridge. I'm not even sure he noticed...but he certainly didn't notice when I did it.
His family is all on him, from day one. I have my own family to deal with. I no longer go to his company holiday parties because they are misery and work and he doesn't recognize it or thank me for putting on a game face for the night. I also only cook dinner when DC home for dinner, otherwise, he can fend for himself. Unless I feel like cooking, I have no intention of doing so once DC are gone from the nest.
I do still plan all holidays and social nights out. If I left it up to him, it wouldn't get planned in time to happen and/or it would just be total crap. So while it's an effort that is completely unappreciated, I do it for myself.
I also make the bed, because I can't stand an unmade bed. DH is 50 and thinks the sheets just magically get washed and changed or, more likely, never gives it two thoughts at all. And if left to it, would just climb into an unmade bed each night.
I do less each year, because even though I keep doing a little less, it's still far more than I get credit for or he does.
And of course, he very, very few things he does do, he must announce, so he can earn his gold star.