If that is how you value their beating the Empire, saving countless lives and buying the galaxy 30 years of peace and themselves 30 years of life, good and bad, life simply because new troubles then arose and challenged them and they heroically stood up and fought those again and inspired others to do so, then I honestly feel sorry for you.
(And, Rogue One aside, if you see "Grim nihilism" in these mostly joyously fun, frequently very funny space adventure movies I think you maybe kinda tone deaf and blind)
-ZacWilliam, anyway that's all a depressing way to veiw the fact that time passes and life happens and heroes keep going and keep being heroes.
Beating the Empire means a whole lot less when the First Order takes over after. It's a very "The Man with an Unclean Spirit" end to the whole affair, you know? Or, in Lewis's words, what good does it do to cast out Mammon when Moloch takes his place?
With the state of the galaxy even before the First Order's victory, it's hard to feel like the thirty years were good ones, with expanded universe material making it worse.
The Force Awakens was a rollicking adventure that had some unfortunate connotations if you actually thought about it, but the Last Jedi is a death march with (bad) jokes. Slavery is unstoppable, good and evil are merely relative, the heroes are almost entirely wiped out, the villains refuse redemption, Luke abandons his ideals, accomplishes nothing, and dies from Force Skyping too hard.
Worse, the film sets in stone the idea of the battle between dark and light as eternal, the Force forever driving a cycle of pain to the point one is tempted to simply say Kreia was right and be done with it.