There are different mental models for how employees work. A lot of people see them like tiers. Low-medium-high tier. In practice people have talents and skills that can be applied in a lot of ways. Erekter set model of employment. People have qualities which can be arranged in a number of creative ways. Judging qualities and figuring out ways to put them together is probably the hardest part, and why employers like credentials. Credentials are a crutch however.