O.K. I do agree that Anduin has some good qualities but here is what I want you all to think about.
Think about the introductory quest chain to BFA, the one that takes you to BFA Boralus, the siege of Lordaeron.
He defeats Saurfang but instead of granting him the honorable death, he arrests him while telling him he is an honorable man…
He is standing there in the throne room, telling Sylvanas to surrender or die. Sylvanas approaches so close and now they are face to face. I mean…isn’t she the master assassin? and he is letting her come so close to him?
The most important quality of a leader is the ability to lead. makes sense? O.K. so what does it mean to lead? It means the ability to make decisions and be Proactive and being the one making the first actions. But as you can see from the scene, Anduin is so reactive, not proactive. He is just waiting and waiting for Sylvanas to make an action…This general sense of waiting and waiting for stuff to happen around him and see how it goes, is what bothers me the most and I think I am quite correct to say he is reactive not proactive, hence not fit to be a leader.
I think Flynn is a middle aged man unlike Anduin.