I'm not really talking about whether something is OOC - because to put it bluntly, it's a fic-bunny which means it's not fleshed out, though it could possibly be done in an IC way but it would take a lot of work and Cloud isn't very sane pe say is this bunny you'll note - but as to WHY so many fans (including myself) have a problem with Tifa is really a singular instance.

Tifa didn't tell Cloud the truth.

She KNEW what he told everyone else had happened in That Incident was a lie. She knew and didn't say anything, but just let Cloud continued to believe an untruth. Wouldn't you be pretty happy if someone allowed - possibly encouraged! - you to embrace a falsehood?

Yeah, so that's why I don't like Game!Tifa. Movie!Tifa softened my opinion towards her and I try not to bash her very much, but there still is that very true concern.