A sole consumer of labor is a monopsony, not a monopoly (that would be a union). At any rate, the point is that there are many many employment negotiations that no reasonable person would agree to amount to duress. This is a counterexample to the idea that any negotiation of employment involves duress. I don't need to disprove the existence of any coercive employment. But SaaS companies are especially relevant since pg specializes in showing people how to become billionaires through SaaS. If earning a billion dollars implies some measure of coercion we should be able to find that in a SaaS startup.
Sorry, misread you — but you can substitute ‘monopsony’ into my comment and I think it still holds.
This is a ‘no true Scotsman’ so I don't think I can really respond to it directly. But I'll point out that my claim is not that some contracts bargaining for safety of life and limb are a form of duress but that all inherently are (to some extent). Especially when the other party's BATNA is ‘no guarantee of safety’.