It's a tough choice, honestly I could see it going either way. It'd be interesting to hear from guys who train. I've never trained MMA, but from my training (mostly from watching the actually good guys), I'd say a 30lb weight disparity requires a significant skill advantage for the smaller guy to compete. In pure BJJ, it's very doable. In most striking arts, it's far more difficult and more rare because it demands a much more unique athletic skill.
Compared to pure striking or grappling, however, MMA isn't as "hands on." Since speed and movement is so important, I think that plays more in favor of a smaller guy's only path to victory against a bigger guy. He would have to outmove his opponent and rely on his quickness and technique to do it. That's Mighty Mouse's game.
The question comes down to what the 100th ranked guy's skillset is like. First of all, I think if he's a specialist at anything, he's more likely to win. If he's an all-arounder, MM absolutely WILL be much better than him, but is that going to be enough?
All I can say is guys seem to perform similarly as they move up in weight. If not better, really. And that's 15 pounds. So the question is whether one more weightclass is just insurmountable. I would guess no, but the fuck do I know.