I'd say it's a mix of Smart, Tatum, and Brown.
Smart is the "vocal and emotional" leader.
Brown is the "get on my back I'm going to raise our energy and physicality for a stretch or a game" leader.
Tatum is the "steady, quiet, lead by example, be the best player but not be too much of a diva to defend, pass, or play within the team concept" leader.
Would it be a little easier if Tatum had a little more of that MJ/Kobe/Bird killer instinct leadership mentality? Yes, probably. But, as is, I think we lead by committee a bit more, and Tatum can still function as a leader just a bit more in the Duncan/Curry mold.