Except that, as mentioned earlier, she's got some of the best white magic based limit breaks the series has ever seen. Take E. Skill, Ultima, KotR, QM, HP+, and Shield materia out of the game. Maxing out Aerith and being able to keep her would have broken the game. Thus everyone who started out on the Aerith hate train and refused to build her up before getting to know her would have been cursing themselves later on because the game would by this time be made ten times more difficult. Of course, that's a hypothetical.