I haven't seen actual professionals say that he will be a premier qb, just that he'll be a very good one. Idiots will say just about anything on message boards.
I'll say it again, Tebow will be a good Ben Roethlisberger type qb who can take a defensively focused team to the superbowl and win. His throwing motion isn't the best on long passes, but he thinks on his feet, makes clutch throws, can avoid the pass rush, and very very rarely throws interceptions. He's not going to single handedly win the game for a team, like Manning, but he won't lose games.
In the end, defense wins championships FAR MORE than quarterbacks. Roethlisberger has more superbowl rings than Manning for a reason, and it's not because he's a better qb.