There's an unproven assumption that somehow the inequality of outcome is 1) unjust, and 2) something to be "corrected."
The first has no foundation other than appeal to emotion to create in-group / out-group tribes ("eat the rich!") to then suggest what end up being power grabs that destroy the middle class and do nothing to the wealthy.
The second item requires destroying value. All economic activity comes from exchanges of value, which is intrinsically tied to time; that irreducible finite quantity to which everyone is subject. We've seen over and over again, when you try to destroy the concept of value, which is subjective and circumstantial for each individual, all you end up doing is causing human misery.
This obsession with taking other people's money rather than enabling opportunities to make your own is unhealthy, destructive, and immoral.
Cool, cool. Work for 30 years, save up and have say $3M to retire on, based on stock market at an all-time high. You're not a robber baron or investment banker, just someone who worked a long time and saved and invested. Govt takes $1M away from you, you have $2M now. Market drops 25%. Now you have $1.5M.
Congrats, your "plan" resulted in someone like that having HALF of everything they saved up just gone.
Yeah, yeah, I know, "if you have $1.5M you don't NEED any more money." Sounds like something that only someone with something less than $1.5M would say.
You don't "need" your iPhone, or your flat screen, or whatever. The government should not be in the business of determining what you "need" and taking the rest.
I'd go further and say that "unearned wealth corrupts" is a well known effect, and (apart from the small subset of rich people who do not care about their kids corruption and intrinsic worth apart from them being the vehicle of their dinasty) we see that divestment into charity / foundations are the modern preferred way for inheritance management, both sparing the kids somewhat (being downgraded to a multimillionaire is not a hellish situation) and gifting them cultural influence. A sovereign fund could scratch that itch somewhat.
Wealth disparity doesn't grow because wealthy people are allowed to retain their generational wealth or not, it grows because the rest can't build and retain their wealth.
This isn't a zero sum game.
PS: I would also not trust the government or any political body to handle income from the inheritance taxes. So I would rather the children of wealthy people squander their wealth, than a politician transfer that wealth to their patron.
thus the importance of the sovereign fund.