Rachel seemed to like Chloe because of her rebellious reputation, and not because of who she really was.

Isn't that just who she is though, by that point? It's not a crime to be attracted to certain personality traits.

it does seem clear that Chloe wanted more than Rachel was willing to give--which would have been fine, if Rachel would have made that clear to Chloe

The way I remember it Rachel was crystal clear about wanting to leave Arcadia Bay with Chloe, and it was Chloe who was hesitant and sending mixed signals to Rachel.

Was Chloe's life better at the beginning of LiS than it was at the beginning of BtS?

Unfair comparison, since Rachel was dead for a while already at the start of LiS. Besides, that was precisely the reason Chloe was so sad. So if that's not evidence that Rachel was everything to her, I don't know what is.