It is the same. Property tax valuation isn't "exactly correct", nor does it need to be. It's just roughly consistent across similar properties. If anything, it's easier to value the private shares you own because they are exactly the same as the shares someone else in your company owns. Properties are all unique.
I don't mean to insult you, but you are clearly not an expert in finance. Like I said, I understand why you don't want to pay a valuation tax on your shares but it would be technically simple to implement.
Honestly though, you don't have to worry about it. No wealth tax is being proposed on any amount under $100 million. And no tax is proposed above 2%. If you have $100 million in private shares, your tax burden will not negatively affect your life. Get an expert.
My favorite story about the gulags is the childhood of Mikhail Gorbachev.
He was born in a family of peasant farmers. His paternal grandfather opposed the collectivization of the farms and was sent to the gulag. His maternal grandfather supported collectivization of the farms, and ended up as the chair of the local farm. He was also sent to the gulag.
https://en.wikipedia.org/wiki/Mikhail_Gorbachev