There's nothing wrong with playing Heavies - see Robert Mitchum, Lawrence Tierney, Lee Marvin, etc.. Jet's problem (aside from language) is that he really has no acting skill whatsoever. Neither does Jackie, really, but his slapstick skills more than make up for it. Jet basically has two options - be immobile and rely on the cinematography/makeup/costume etc. to make him appear menacing, or be immobile and rely on all that to make him appear noble. Expressiveness is simply not an option, as far as I can tell.