Raoul usually get played as a nancy-boy, which makes him a pretty dull contrast to Erik, who is a compelling, complex and ultimately tragic figure. True, he's a psycho who garroted Buquet and Luigi, and who was more than willing to blow up Paris if Christine wouldn't choose him, but -- especially if you've read Leroux's book -- you can't help but feel sorry for the poor bugger. And Lloyd Webber's musical makes him a compelling, mesmerizing figure. All Raoul does is react, and he's always playing catch-up. Erik not only exists in Christine's world, he exists for her.
Raoul could be a better rival to Erik, but I've never seen him portrayed that way. The closest was in the Claude Rains movie, but even there, he was a rival with a baritone in the opera, not with Erik, whose role was stripped down