Revolution may or may not improve things for the underclass, but it certainly ruins things for the upper class -- at least they are forced into playing political games all over again and cannot rest on previous political success (though, yes, if they are trained or predisposed towards politics at least they have a chance). And the credible threat of revolution forces that cool, calculated, and orderly effort to go somewhere, instead of merely watching the arc of history bend as slowly as the earth's surface.

Britain, for instance, was not irredeemably terrible during the American Revolution, as evidenced by them being basically as reasonable a place as America today and not having had a revolution of their own since then. And they even managed to do some things better (e.g., they banned slavery before America did). But the American Revolution was still worthwhile, and that gave credibility to the American approach instead of the imperial one.