[humanrebar]

Let managers release under-performing developers to "the bench", where they can be picked up by teams that need some new blood. People on the bench are cheaper to "hire" than people from outside, so managers have an incentive to prefer picking them up.

Managers don't "let" developers do anything. They have to actually have leadership skills (or enough budget) to keep their good engineers around by choice. Effective developers on poor teams find more attractive offers. Sometimes this will involve bonuses or raises. Sometimes this will involve more influence over product direction.

Obviously some sort of ground rules are needed (significant others on different teams, no kickbacks).