To approach this from a different angle, I think that KB is primarily like Sam Raimi, in that he is an actor's director. A script that focuses on character driven story, such as the Spiderman movies, works well in the hands of such a director. While KB can clearly direct scripts with larger plot concerns, Shakespeare is, at its core, about the characters and their growth or decline. If the Thor script is mainly plot-driven, then the producers may have wasted their money picking KB to direct instead of some action movie director with big FX experience.