Marvel Studios has forgotten this crucial lesson from the first Thor movie

Before he was cast as Superman, nobody knew who Christopher Reeve was. The same was true of Hugh Jackman before he played Wolverine. Yet in both cases, the casting choices were so perfect that those actors managed to define their respective characters for at least a generation, if not more. If anything, their lack of fame was an asset to their casting, as it allowed the audience to just see Superman or Wolverine in a way they may not be able to with more established actors.