I am not sure where you are getting your information, but this is false as far as I can tell. Even if it were not, treating Muslims like infidels is infinitely worse.
That
is part of treating Muslims like infidels. The jizya tax is derived from non-believers but it was being applied to non-Muslim converts. No one said it was the only reason but it is the main reason because it highlighted that the Umayyad authorities were not following Islamic law and their obligations.
Oh, there are some hadiths condemning taxes
Yes and they are pretty much accepted by most Islamic fiqhs. Islamic law explicitly condemns income tax, or maqs, and Muhammad abolished the maqs and declared it a major sin. Regardless of whether or not you believe this is a faulty interpretation doesn't change the fact that the Umayyads adhered to it or that the vast majority of scholars, including today, viewed the extra taxes imposed by the states after the Umayyads as tyranny or tagha. As such, for the purposes of analyzing the historical causes of the failure of the Umayyad state and what informed its policies it is worth noting.
Ultimately, this specific supremacist policy is a matter of economics due to the constraints the Umayyads felt for their own religion. As such, they had to either break with Islamic law, try to find loopholes that did not produce enough revenue, or simply keep getting loot which was the primary method of obtaining revenue.
The same place where I encountered said hadiths states that they pertain to taxes levied by tyrants, unjust either in their purpose or their amount.
If we are talking about the same ones, like those narrated by al-Nawawi and Ahmad ibn Hanbal, then that is not true. It isn't permissible to take the wealth of any Muslim without consent and, moreover, income tax or the maqs is the most evil sin of them all. So I think it is pretty unambiguous overall or at least understandable why most Islamic scholars and Muslims, including the Umayyads, came to the conclusions that they did.
From the cursory research I have done on the topic, the state can pass laws of any nature provided that they not be unwarranted, and that they do not conflict otherwise with jurisprudence. This naturally includes taxes.
Well yeah the underlying problem is that applying taxes conflicts with jurisprudence. The only valid taxes are those on land but that isn't understood as a tax insofar as a service whereby the state serves to defend the land. As such, the state is conceptualized here as a sort of protection racket but with limited authority over the wealth of others. Islamic law covers a lot of areas and imposes restrictions on what laws the state can pass.