I think there's a really easy explanation for why Thor is shown as less powerful. It's the same reason Superman doesn't unleash, Thor would would/could cause too much damage to the environment or others if he went all out, and if any of you play sports or have fought, you should know going half ass never yields good results. So, just think of it as Thor going half ass for the benefit of Earth. We all know how nasty he is when he's on a planet where he's not worried about casualties. Just ask the frost Giants.
I reckon, we'll see Thors true power forthcoming.