don't forget slower, not as tough and he's not very good at getting up from his back. Bonnar put up a better fight than Moussassi would, most overrated fighter there is.
I don't think his particulary slower than Shogun and where did you get that toughness comparison? Mousasi hasn't been rocked before. Never been finished due to strikes before and is no slouche on his back. The problem with him is he goes to fight, not to win a contest. Hell, he did more damage on his back to King Mo than he did on top.