Football requires a player to go all out on each and every snap if you play on either side of the line. Mario isn't that type of player and it looks like he goes in and out of being engaged.
He's so physically capable of dominating that, when he's in it - watch out, he can ball. The issue is he doesn't have enough passion, IMO, to ever truly get the most out of his physical ability. When he gives enough, you can love his game as a fan - when he's not giving max effort he's one frustrating SOB to have on your team.
Mario is a power rusher. His main move is to bull rush and then use the swim move late depending on where the QB is located at that time. This requires an extreme amount of physical effort. The contrasting speed rusher ie, Hughes - takes more stamina/endurance. They're both mental grinds and both player types have to commit.