Here's the thing. When I first read the scene, I thought Mikasa family-zoned herself because she got nervous, and was afraid of being rejected by Eren. I think she was still in love with Eren and cared about him, but she was afraid that if she told him that he wouldn't return her feelings and she'd be heartbroken.
I know that Eren was clearly hoping she felt that way about him and was obviously trying to convey that to her, and I sort of feel like she knew that too, but when you're that infatuated and in love with a person, you tend to doubt yourself and get incredibly nervous when it comes to telling that person how you truly feel. Even if they clearly feel the same way about you.
I know that I'm giving Isayama way too much credit here, but if I absolutely had to give him the benefit of the doubt, I think her suddenly family-zoning herself has more to do with the above reasons and not just author fiat.
Ya know, unlike her and everyone else ignoring Eren's obvious depression, PTSD, and declining mental health. I take a lot more issue with that personally.
The thing is that most people wouldn't be supporting him if the entire world wasn't also absurdly racist to the point of being a-okay with holocausting his race. That's the problem.
All he had to do was just have Eren assume everyone else hated his race because of the limited terrible experiences he had with the KoM, and he just naively thought that the entire world was just as bad and hateful as them. It would still be dumb, but at least it would make more sense than the entire fucking world hating his race to the point of wanting to genocide them over what happened to some pigs two-thousand years ago.