You've forgotten the core tenet of every engineering discipline is the master-apprentice relationship. The reason why what you describe is really the gig economy is because you've turned contractors into autodidacts to cut costs. You're not only expecting engineers to work for you, you're expecting them to learn their craft without capitalizing that yourself. Someone has to pay for that too; it probably won't be your other contractors -- otherwise you'd be something like a real company again.

Your success in this direction to turn software development into some kind of cattle feedlot is only a mirage. Let me make it clear in economic terms: you're up a few chips at the casino, for now, because the market allows you to be. In the long run it's not sustainable, and won't yield any major feats of engineering with any level of competence.