1) No, I did not compare them. Seriously, go back and read it; I am criticizing your moral standard, and gave a clear example to show where it fails. But in case you're still worried: no, Uber is not much like a Ponzi scheme.
2) That is not "exactly like freelancing". It is more akin to the company town approach to things, where the nominal structure of freedom is used to wash away moral responsibility. And if you talk to ex-Uber drivers, they do not feel there is a "whole range of options". Uber claims 87% market share, making them by far the dominant company. And the notion that Uber aspires to be a monopsony is not my assumption; investment analysts looking at Uber are pretty clear that Uber's market valuation only makes sense if they end up totally dominating things. Really, I freelanced for years, and two of my parents did as well. Trying to tell me that Uber is particularly like freelancing is pissing on my leg and telling me it's raining.
3) Uber is clearly the more powerful party in both the contract law sense [1] and in the market sense. There's no "somehow" here. They are the ones who write the contract. They are the ones who set the terms. They are the one who can unilaterally change the terms. They are the more powerful party. So get out of here with your "somehow".
4) And as to the leasing thing, I begin to be concerned that you're not arguing in good faith here. Uber literally helps people lease cars full time, so I think it's reasonable for people to read that as Uber suggesting that full time is reasonable. You after all brought up leasing.
More broadly, you're making the sort of tendentious, over-narrow arguments that were used to justify all sorts of exploitative behavior before labor laws required people to be either employees (therefore deserving of protection) or true independent contractors (who are professionals and can deal with things on their own because they operate in a functional marketplace with multiple clients). The last couple decades have seen businesses creeping around those barriers because it lets them take advantage of power asymmetries. I think Uber used a weak economy and a technological change to further undermine those barriers.
If you want to make a serious argument here, you can't just sweep Uber's enormous advantages under the rug. There are giant asymmetries in information, legal resources, negotiation skill, market power, financial resources, manipulative skill, and political clout. If you'd like to make a might-makes-right, fuck-the-workers case, just go for it. But if you're going to continue to make an argument about fairness, you have to account for power. Otherwise you're just ignoring a century of labor and employment law history.
[1] See, e.g., https://en.wikipedia.org/wiki/Unconscionability for how power is relevant to contract law.