But that "peace" comes from him (or, rather, his family) murdering anyone who disagrees from them. Peace isn't much fun when you're dead....
Not really.
At least Rin's world has the potential to develop into something better. Leo's will forever be stuck as an oppressive fascist dictatorship, until someone like Rin comes along and overthrows it, at which point it becomes like Rin's world anyway.
Nah, she's exactly like normal Rin, from what I can tell. Acts like an uncaring bitch on the outside, but is actually rather nice when you get to know her. OK, so her "ideal" is pretty fucked-up, but so is normal Rin's. It's just that Extra Rin doesn't get the same opportunity to overcome it that normal Rin does, because of the situation they're in. Although, IIRC, she doesn't try to convince the MC to grant her wish if he wins, so she must mellow out at least a little.