If it's true that the "owner" is merely "extracting" value from the "productive" workers, then the productive workers should have no problem setting up shop for themselves. This is a consultancy we're talking about; the way you've framed it, there's no barrier to entry for the exploited consultants to set up competing firms with better terms for developers. In fact, they don't even really have to set up firms. They can just all quit, operate as sole proprietorships, and subcontract back to the owner's firm, who will have no choice but to 1099 them, at floating rates, when all their workers leave.

That this rarely happens in practice should tell you something about where the value in an established consultancy is generated.