It's ironic that a number of former Soviet countries have moved on to the flat tax, while the west has a progressive income tax (#2 plank of the Communist Manifesto).
Idk about you but I can't think of many former soviet block countries that have a healthy distribution of wealth between working, middle, and upper classes. Furthermore the list of countries given there are not places where you want to be poor.
Are you saying that flat tax is good, but that all countries that have implemented it coincidentally have other economic issues that are wholly unrelated?
Romania and Poland were never soviets. Communist, yes. Behind the Iron Curtain, yes. Members of the Warsaw Pact, yes (Poland is kind of obvious on this). But never soviets.