I think the basis of hate Mei has been receiving is based on perspective, really.
I've adored Yuzu since the first ever chapter and I grown to love her even more now, with Mei though, there's something that never clicked with me and her. Maybe because I think she's an individual who refuses to love and be loved
Flip it around and you notice that Mei is misunderstood, she loves Yuzu, you cannot deny that she does, even says it in the letter in a subtle way. She was just being selfish all these volumes because she yearns for Yuzu's love but could never truly accept it and be with her because of her "dreams"(I call it an arranged obligation)
I do think Mei made a rational choice with the letter and then secretly leaving but I'm worried for Yuzu. First she's incredibly sensitive and probably had to deal with suicidal tendencies and depression when she recieved the letter and she'll find someway to interfere with Mei's "dream" again.