I actually fully understand Thor not being as powerful as before without Mjolnir. That weapon provides all manner of exotic abilities that Thor himself can't really access.
However, I've always wondered about the metal arm, does that arm have the strength that Thor would have normally? Somehow, I doubt it.
It's just something I've noticed lately because Thor does seem ....weaker than before. He got his head fractured by Hulk and apparently Namor is around his level now (or above it now). I know he defeated the Juggernaut off panel but he just seems a little weaker than before.