Thor is hitting the Hulk with a super-weapon. Isn't it only fair that the Hulk get to strike Thor with a super-weapon as well?
Or does the Hulk simply not need a weapon as a crutch?
Thor rarely uses Mjolnir for anything but a striking weapon. What little extra damage this does is more than balanced out by whatever slight strength edge the Hulk has PLUS powerful healing factor. In many fights the Hulk often does not so much outfight as he outlasts his opponents. Mjolnir is such a part of Thor that it is like Captain America's shield or Batman's belt. To say Mjolnir is a crutch and Hulk needs a weapon to make things even is about the same as saying the Hulk's healing factor is a crutch and Thor needs just as powerful a healing factor to make things even.