The idea that Luke, Leia, Han, Lando and the Rebel Alliance generation achieved nothing because of the ST is ludicrous. They achieved nearly thirty years of peace and freedom. The First Order then only takes control of the galaxy for about a year before they and the Sith Eternal are defeated. For all of real human history there have been periods of war followed by periods of peace, ultimately followed by periods of war, and so on. Just because the OT generation don’t succeed in ending all war in the Star Wars universe for all time doesn’t mean what they did was pointless. TLJ is quite explicit in its theme of “we are what they grow beyond” - one generation can’t fix everything, but so long as each subsequent generation can learn from some of the mistakes of their ancestors and move forwards, we ultimately achieve progress. Just like real human civilisation.
Well, more like ten years if you take into account that most of the First Order soldiers were kidnapped as children.
And according to the Mandalorian, those first five years still had the Empire in control in the outer rim with the New Republic struggling to keep control of just the core worlds.
So yeah, the Core worlds had it good and the rest of the galaxy did fine for about five years as well.