You know The Rock was only 2-years into his career and was still improving when he got the World title, right? Same with Cena. Same with Orton. Same with Batista.
Apparently I'm not allowed to compare the Miz to The Rock, because that's unfair. However, if I were, Id say that the Rock had a) had time in the USWA long before he sniffed the WWE working with legends and gaining more valuable experience than the Miz got with working with nobodies in OVW and b) it's in his blood and he's been around it his whole life.
Let's compare the Rock to The Miz shall we? The Rock walks, talks, and acts like a star. Miz, while getting better, walks, talks and acts like a guy who is trying to be a star, hence why he has to take ACTING CLASSES. He's not a natural, and if you're going to give a greenhorn the title, give it to one who's at least a natural, not someone who needs to take classes.
Sometimes, you just have to give a guy the ball and see what he can do with it. Has Miz hurt the company in any way since he became Champion? Nope, quite the contrary, he's actually helped them. Look at how much media jumped all over the story.
If the Miz was never on the Real World, no one would care about him. This is, I think, one of the only reasons the guy got the title. It has nothing to do with him being good, it has to do with his Q rating, and how much play the WWE can get from it. Forget the fact that he's not one of the top 10 stars in the company, "Dude MTV and EXTRA will jump ALL OVER IT!!" Great short term reasoning, shit long term vision.
And yeah MS: JoMo is a strong character, ask the fans who saw him drag Sheamus to a passable match as he was the only one garnering a reaction.