I agree about wealth cap. I suspect that ultra-rich would rather pay higher taxes than have a hard cap. Or cap will be defined in such way as to become meaningless. This is why I advocate for high tax brackets, as being more realistic in practice.

As for proportionality - taxes are inherently unfair on the individual level. But they are fair on the large society level. All of our niceties are essentially funded from taxes. Current "free market" plus corruption mean that to finance growth more and more money is needed and part of them come from more and more taxes. But a lot of basic goods are fix price or low enough price, so that they make le and less percent of person expenses the more income rises. So to be more fair, it is fairer to increase tax on the ultra-rich class and spare tax increase on poorer classes, making average suffering lower. If we simply increase all taxes, then the lower the income the more tax a person would pay. It in kinda unfair and not productive to do it this way.