Trying to define buckets with arbitrary thresholds is futile.

It greatly benefits the top outliers, since the top bucket will have a huge disparity between its strictly defined lower bounds, and an infinite upper bound.

There's no need to "define rich". A formula without defined bounds (this is the most important part) should determine how much tax you pay, and it shouldn't discriminate between different forms of income. More importantly, all net worth gains should be taxed equally.