Super high earners don't earn W2 income. It's mostly long term cap gains or gains in tax advantaged accounts. A 90% tax would just encourage them to never sell their stock and to borrow against it instead.
What happens when the stock market is up one year and down the next?
What happens when you force them all to sell and there is not enough liquidity to support current prices so the act of selling hammers the value?
You are just saying "let's slowing take equity away from founders" so we can throw it away into wasteful gov. spending.
But seriously, inequality is a complex issue, just 'let's soak the rich' is a dumb take and won't solve anything.
But social safety nets, estate taxes, single-payer fed health insurance, etc.. might be interesting as well as other ways to approach this. For example, maybe corporate tax rate should be ZERO, but some percentage of profits (let's say 25%) should be paid as dividend to employees.
I believe the things I believe because I think they're the best things to believe (acknowledging my imperfect knowledge, potential for errors, etc). If I thought something else was better than what I believe, I would update my beliefs towards that. If you don't think your beliefs are better than the alternatives, you don't actually believe in them.
So yes, I think my goals are the best possible goals to want.