I've long advocated for building a candidate pool for both hires and promos from a low baseline (with the option to opt out for promo), then hire/promote random

I've long advocated for building a candidate pool for both hires and promos from a low baseline (with the option to opt out for promo), then hire/promote randomly out of that pool. Then fire/demote based on demonstrated incompetence. The important thing isn't that you promote the best worker; the key is that it isn't possible for the ambitious-but-incompetent to game their way up.