6) Cloud and Aerith only knew each other for 2 months.
Closer to a week actually, from what I can tell.
If I remember correctly, the game starts on the 9th of december, which would mean he falls into the church around the 12th of december. Aerith probably spends a day or two in Shinra HQ. And by the end of december Cloud has already given the black materia to Sephiroth from what I've seen from the timeline.
That leaves about 2 weeks for them to get to know each other, her to die, and have the subsequent journey to the northern crater and mental breakdown. If that takes about a week, that leaves a week to 10 days with Aerith.
That's, and the fact that Cloud is braindamaged is what realistically makes the ship not work in any real life scenario, it's just not realistic. That wouldn't be love but a strange sick obsession.
But more importantly to me, it doesn't work as well with the themes, narratives, and plot of the game. The story is inherently not as good with Aerith as the love interest.
Specifically it makes Aerith a less interesting character because it removes a lot of her inner struggles. One of the reasons I prefer Tifa as a character is because she has more going on internally when removed from overall conflict.
If Aerith is going through an internal struggle concerning her love of Zack, her confused feelings for Cloud, the loneliness of losing Zack, and doubt about what she feels etc, then that's a good story, and her falling in love with someone because he's literally her ex's living legacy works extremely well.
But in the Clerith version Aerith doesn't really have a good personal story, Zack is diminished to the status of someone who really doesn't matter much anymore, in which case, why is he even part of the story? The story of "I had an ex, but I am over him now and am with this new dude", inherently is devoid of meaning. It also requires you to accept that the fact that the next guy she likes literally being her ex's living legacy is basically just a coincidence....which, would be absurdly poor storytelling.
She just happens to like the real Cloud? Even though she's never met him? How convenient :S
Unfortunately for the Clerith interpretation, the idea that Aerith is simply over Zack is less interesting than the idea that she's trying to convince herself of something she doesn't believe. That doesn't disprove it, but in writing, you generally don't add in things such as these unless they have an impact on the story. It being irrelevant would be bad storytelling, and I don't think FFVII is a poorly told story.