McClain is a stud, no doubt, and he can dominate on a play or a drive, but Suh dominates and controls whole games. He leads his team in tackles from a defensive line position....that's not normal.
To be a defensive player and be considered you can't just say "hey, why not this guy, he's really, really good"...you have to say "I've never seen anything like this", which a lot of people say about Suh (right or wrong, as people tend to forget the past...like Lawrence Taylor at UNC or even Mario Williams from just a few years ago).
But the point is, Suh makes you say it, McClain doesn't.
Take McClain out of the Alabama defense and it probably costs you some yards on a few plays here or there. Take Suh out of the Nebraska line up and Texas probably scores 35 points as McCoy stands in there and does his thing.