All right, first off, you can see in the description that it says "Erica." Maybe it's legally still Eric, and since a lot of people already know she used to be a he, they aren't bothering to hide it.
There's also no given evidence that it's the best ending because she never transitioned. For all we know, he simply identified as male in that timeline, so there was no need to transition. Not that he was struggling with the decision, and was convinced against it. Or maybe he was and it's presented in a way that's not worth the outrage. I don't know, and I don't think you really know.
I think there's plenty of other things to be angry about: Like how, if you can change the timeline for the best, why she's not born as a woman to begin with. Or how in the original game, her transition only exists as a punchline because there's a male character that's trying to hook up with her the whole game.