Bowser, Charizard, and DK are the heaviest characters, but among the faster running characters. Only Ganondorf and Triple D are the slower-moving heavyweights. I can't think of a reason for Ganondorf other than stopping him from wrecking people, but running that slow... Triple D at least has an excuse for packing living metal spikes somewhere in his robe and carrying a hammer with a jet engine installed. Charizard has functioning wings even though they look kind of small and DK's a gorilla who are fairly mobile. Bowser, I guess you could say he's used to his weight and he actually considered strong in his home series, so he's probably "muscular" and "athletic", but no in ways what humans can relate to. At the same time, he has a shell... He's a turtle. That amount of weight... Then again, you have Falco and Wolf running slower than many other characters despite them looking well-built - you can actually see Wolf's biceps on his model. I blame game design choices.