You say he is a leader but he really hasn't been anything close to a leader up to the
palace, which is where I am right now. There hasn't been a single moment in the game that made me think "Now, that's how a leader thinks/acts".
Thus far all I've seen from Joker, is just an extremely unimportant character, who is just there to take the blame if anything happens. He has close to zero input as to what actually happens within the Phantom Thieves. I'm talking about story stuff, but even something like going to Metaverse is an unanimous decision and even though no one ever disagrees with you, but storywise even that's not Joker's decision.
Again, maybe my opinion will change as I progress through the game, but right now at this moment, Joker is simply a joke side character that the game is trying to sell as some important guy.