An exit tax in itself does nothing to prevent hoarding of wealth. It might enable you to deploy other taxes that would make rational people leave the country, but it's a bit of a "lock the doors and rob people" strategy.

If you have good advisors as a wealthy person you know this and leave as soon as an exit tax is on the table. If you start new businesses you start them outside of the country

If you're a regular non-wealthy person who happens to become successful you're stuck paying high taxes of course, but you'll probably learn and structure your next venture better.