Lor'themar has been a leader in the Horde longer than anyone else, including Baine. He is one of, if not the biggest presence in the Horde at the moment.
It only looks weird because he's the only one, with Baine absent, which says a lot more about the state of the Horde than it does about Lor'themar.
He's also in Zandalar quite often, especially in Nazmir, though even there he still comes across as a follower and not a leader.