Having read the OP (took a long time
at least it was intelligent)...
You've convinced me that there was some thought put into her character, the fact that the character dies, with a specific timing and location. Thinking about it that way, there was a special impact to her being killed in the Forgotten Capitol, in a very... tranquil scene, I want to say. (No music, quiet sound effects... and then the sick fact that you have Aerith's joyful theme playing throughout the moments that follow. That, in particular, defined the "pathos" of the scene.)
To me, it would've been more obvious to make Cloud kill her at the Northern Crater after giving Sephiroth the Black Materia, but even that wouldn't have been dramatic enough. The way they did it was nearly perfect.
However, the stereotypical Sephiroth-haters (the ones that say, "He killed a flower girl, Kefka killed Cyan's family, hurr durr!") would never come to truly appreciate what the scene is about. I mean, no one really cared when Cyan's family died. No one really cared about anyone Kefka successfully killed. Please catch me out if I'm wrong there.
Kefka is just about global disaster - if we really cared about that, we'd actually try to stop global warming
No, for us to really react, we need an emotional attachment to whatever's destroyed, and the Aerith-killing scene played on that very effectively.