Sorry, rant coming. (I assure the mods this is impromptu and not copy-pasted; verify yourself.)
I don't see a lot of productive progress being made on this question. Judges constantly try to apply conflicting standards of whether someone is "really" an employee, but you can't make progress on that question until you can measurably answer why you're asking that question to begin with.
For another context, take "is alcoholism really a disease?" If we don't want to be stuck in unproductive talking-past-each-other, we have to transform that into a more concrete query, like, "are alcoholics responsive to social pressure?" or "does the urge to drink stem from a chemical imbalance?"
Those questions, you can actually -- in principle -- make progress on. Maybe you find some chemical under which alcoholics stop drinking because it doesn't appeal to them anymore. Or maybe you find that shunning changes their behavior, and the appeal to "alcoholism being a disease" maps to a specific game-theoretic strategy.
Or maybe shunning just turns out to make alcoholics miserable and resort to more expensive, covert techniques to get their fix. Or maybe the evidence is perpetually ambiguous. But at least you can make progress on those questions.
What are the corresponding criteria for the question "is this Uber driver really an employee?" How would you know you got it wrong? What are you really optimizing for when you legislate a distinction between contractor and employee?
For example, let's say you proposed a new test A, under which every purchase of labor makes someone an employer and employee. You buy a haircut? Great, you need to send this amount to this fund to pay for their unemployment insurance. And you need to give them this notice about their rights as a worker. And you need to pay into this worker's comp fund.
Or let's say you proposed a test B under which the buyer is the sole decider of how to classify, and every employer/buyer in the world elects to classify the provider/worker as an employee, and screams in glee as they offload all the liability and expenses onto the worker. By what standard, concretely, do you know you erred?
It doesn't work to say "that's absurd". What's important is to say the specific desiderata that make that situation absurd.
I have yet to see someone propose a (satisfying) standard/desideratum to ground the employee/contractor distinction in law. The closest I've seen is "we want to make sure workers don't get oppressed" (or some equivalent expression), but that doesn't suffice -- there has to be some reason you don't go with the A test above. What is that?