When you bring your A team to a project, you are doing it to make sure your project is a success.
It’s an important project and you have picked the best project manager, the best technical lead, the best coders, the best resources, the best specifications laid out, so on and so forth, making sure your project is a success to start with. But if none of them is taking accountability of the project they can bomb the project.
To make project a success, at least someone if not all, has to stand up and say if something is not working, the meetings has to be where the team members has to make sure the project is moving in the desired direction and if not, raising the concern, and asking for the change and moving forward only when it looks good.
When accountability is taken, mediocrity ends. Bringing the best is not enough.