Except Beast doesn't lead. He doesn't pay attention to the situation. He is in his own science-world. Look how he was behaving when they went to meet that new mutant.
Not the same at all. A field leader isn't followed because people like him or because of his conviction. People follow him because they have to and because they trust his skills.
But to get people to sign-in for your cause. To risk their live for an ideal, you need wholly different skills. It doesn't matter if you don't have any tactical skill : that's why you have other expert for. What is matter is that you can get people to follow you. To rally around a common cause and fight for it.
We are just not talking about the same kind of leaders
I agree that Jeen (or adult Jean for that matter) will never be the best field leader : for one thing, if having to choose, she will make the "moraly right" choice and not the most tactically sound one. Except in very rare occasion, she will always try to talk first even if that's a mistake.