MEGA push? He was getting a very good push, but let's not pretend he was getting pushed like Brock Lesnar or Triple H. The only major thing he had done is a feud with Mysterio, and I'll grant you that Mysterio is a main eventer, but he's a B list main eventer. He's not an A list main eventer like John Cena, Triple H, Undertaker or Randy Orton. He's not even Edge's equal. I had him pegged to win MITB and that was a much more realistic situation to most people than winning the Royal Rumble. Sure, he kept saying it was his destiny but that type of bragging is typical for a heel. Most people figured that he'd get eliminated by Rey Mysterio and he'd blame Rey for costing him his "destiny".
I agree that Sheamus going over Cena was surprising, but it's hardly the most surprising thing. The way it was set up made it completely believable with it being a tables match. Plus, Sheamus isn't a commentator or a woman or a 3 ft tall midget, he's a huge, grown ass man who's ripped. He might not have been anywhere near Cena's level but the fact that he could handle himself is more than enough for me to say it's reasonable to suggest that him winning the title is not the most shocking thing that's happened ever or even recently.