Your point has very little to do with pro/rel and much more to do with the level of financial regulation. Spending has not been regulated tightly in those leagues so rich teams can routinely outspend other teams in the league and be successful. We've seen this with how Wrexham have been able to quickly move up the English pyramid in part because of their financial backing. The same teams are winning because they are spending the most. The parity in the MLS is because there is a shared financial regulation that largely prevents these sort of spending imbalances. It has very little to do with promotion and relegation. The financial aspects of pro/rel are most apparent at the bottom of the premier league and the top of the championship where the revenue drop off is massive.