I don’t think it’s technically true that your shares in your company would be worth a multiple of what someone else paid for their shares when your shares were valued as part of your overall wealth for tax purposes.
No, it's a bad hypothetical.
No it isn’t. That’s exactly why taxing non realized gains isn’t common around the world.
As above, it is common. See: property taxes and mark to market. It is perceived as being administratively infeasible because the folks who would be paying the biggest bills want you to believe that.