Open source is a way of coding, which still requires a centralized management. If the management is inept, no amount of free coding will fix that. For understanding these concepts better, I recommend reading about
Cathedral and Bazaar coding.
However, you are correct, I doubt anyone on the current staff knows the game well enough to create a vision much less implement it. That's never been what PA staff was chosen to do, and thus non of them have ever been capable of doing such things.