I can understand where you're coming from, but that's hard to do. I ride an R3, which is the same price as an S2. I'd be on an R5 (analogous to an S5) if money was no issue. So my answer is that the S2 and S5 are very similar, both bought and ridden by the same basic type of rider as far as style and purpose go, but that the S2 is for the more budget conscious among them.

Ironically, though, I think a lot of people in this forum would prefer to race an S2 vs an S5, because crashes are more likely in a race than a solo ride, and, again, because of budget reasons to do with replacing the bike.