There seems to be a lot of people coming from the position that poor defensive player can't be a good leader.
I don't really see it that way, Brady does a lot of things on and off the ice that support the premise that he's a strong leader.
It's been widely reported that he's doing a lot of the little things to make guys comfortable when the join the team, for example being first to reach out to new acquisitions, being there when the join the team for the first time to great them as the arrive at the arena, he says the the right things in interviews, for example when Sogaard let in a bad goal and took responsibility for the loss a few weeks back, Tkachuk was asked about it, framed in such a manner as to discuss how mature Sogaard is, he instantly made it clear the loss wasn't on Sogaard and said they would talk to him and sort that out, make sure he understands.
On the ice, he's the fist to stand up for pretty much anybody, he knows when the team needs a boost and how to change momentum, or get the guys going.
He does all the things in the community a leader should do too.
Honestly, if you're questioning Tkachuks leadership you better have some sort of insider scoop to back it up because pretty much everything in the public eye suggests he's doing a stand up job.