But don't they?
No.
If one player says to another: "No, no, don't go that way, you'll provoke an AoO. Come around this way and then flank the devil cause that way, I can use my xyz power as well", isn't this effectively deciding what someone else's PC does?
It's a suggestion. The player still chooses what he does. Basic social interaction. People talk to each other and express opinions.
Not directly, but it's group mind. The individual does not always make his own decisions, he relies (and maybe even becomes dependent) on the group to decide.
If he prefers it like that, that's fine.