A union is not a coop, so the forces are not the same at all.

Furthermore, it's not clear that "seniority" would trump "skill" in a co-op, either. Or that the opposite is true of a more "traditional" workplace.

The job of each worker-owner is, in part, to help other worker owners developer their strengths to their fullest for the benefit of co-op.

An employee-owned co-operative corporation (EOCC) governs as form of direct democracy. In my experience, your biggest obstacle is going to be collective decision-making. How well you do that is a test of the people in the co-op. Consider: management is just another skill, not a rank. You don't have a boss. You have people who are counting on you. Management serves at the pleasure of the worker-owners.