When the group is "the most successful in the current system", it's not exclusionary / discriminatory or exploitable. Whether their success is due to luck or smarts or inheritance, they succeeded in the current system by definition, because there is only one system. Therefore, they can be asked to pay proportionally more to maintain it. Furthermore, the bargain "to pay less tax, be less successful" is not one that any rational actor would make. It's inherently fair.
The only part you could reasonably quibble with imo is using wealth as a measure of success, but since it is the currency that taxes deal in -- one alternative: government takes some of your children -- it's the one that makes the most ssense. Still, those in society that find some way to life satisfaction without accumulating wealth do have an advantage in the proposed system. Maybe that's something we should encourage?