> In some ways taxing wealth is quite simple

But there are enough other ways where it's really hard and unsolved. Imagine someone bought an $X irreplaceable ancient urn to hold the ashes of their parents.

How do you calculate the $Y "wealth" inside that non-fungible urn on their mantelpiece today? How can one determine which "I would buy that for X" statements are falsely low or falsely high?

> owners go out of their way to estimate the magnitude of their wealth for example to borrow money

I have no inherent problem linking one voluntary claim of wealth to another conclusion of wealth... But what happens when someone wealthy who doesn't actually need any loans applies for them while presenting themselves as a pauper?

Or cases where someone seeks a loan and their rationale is "I may have negative net worth but you'll be made whole because you're first in line", as opposed to "I have high net worth"?

> I have a hard time to find a good faith reason for capital gains to be taxed less than labor.

Consider a small company of AcmeCo with 1-10 workers all dedicated to the art of Acme'ing, each taking tiny wages (but accepting shares) because they believe in the mission and want to launch the company.

On a technical level, anything they (might) get would be capital gains, but clearly it's not the same as passive rents with no labor behind it. It's closer to deferred wages.