I think Irvin wants to be that guy, but folks seldom realize it's not a matter of who wants to lead, but who the players want to follow.
In my youth coaching experience (not something I bring up a lot, so please bear with me), I've had some great kids be leaders of my teams some years, but other years it has been some real Richards who the team has followed (often to our detriment).
The toughest years, though, were the occasional season when the team didn't follow anyone. No one stepped up and took the mantle, and when anyone tried to do so the team wasn't having it. I've been worried that this Michigan team is like that.
Leadership is unpredictable like that. It's great when it comes from your most talented players, the ones that other players naturally want to be like. It can come from among your least talented players, if they are the run through walls type who can turn to the rest of the team and ask "I'm giving my all. What's your excuse?"
It's tough, however, when a player who should be a leader isn't leading so much as they are trying to lead, dipping their toes in those obviously uncomfortable waters. Those kids seem to be the ones who get really quiet when their performance is slumping, like they feel like they don't deserve to be the leader, and you can't have that. Your team still needs players who lead.