I actually liked when Thor and Blake were joined, made for interesting stories!
As a surgeon, there were things that he could do that Thor could not!
Depends on which writer. There are instances of Thor using Blakes' skill. There are instances when he changed back to Blake to perform surgery especially in the Lee\Kirby years. However I do not know if that was because Thor lacked the ability or in order to protect the identity plus a god in the hospital would bring a lot of questions. Have you read the early stories or only the post Lee depictions. I envy people who are reading them the first time.