This is interesting, and I really admire Radcliffe, but I've never seen him play a borderline psychotic character. In that vein I think I prefer Elijah Wood who not only has already been pre-shrunk to Hobbit size (thus saving the production company a bunch of money), but has already done a delicious turn as a guy who wants to cut everybody up in "Sin City". Thanks for the inspiration, as up until now I haven't been able to visualize anyone as Beltar.
To support your point I submit: Superman and (the original Fawcett) Captain Marvel. I've always thought that there was no reason on Earth for these two characters to be depicted as over-muscled, since they rarely have to strain themselves and therefore their muscles would never have the opportunity to become damaged and repair themselves, which is what creates muscle bulk.