I hope someday Lucas’s treatments do come out, I’d be curious. But knowing his past writing processes (on the OT and PT), it’s more likely than not that his treatments were pretty short and vague. More importantly, even if Lucas himself had made the films he would have certainly changed the story of his treatments significantly over the course of time. So the idea that they should have chained themselves to those treatments just because they had Lucas’s name on them is monumentally silly.
More importantly, the idea that evil will always return is “nihilistic” is ridiculous. It’s just factually true. The idea that evil can be defeated once and for all is pretty naive. It works for a fairy tale yes, but Star Wars has been becoming less and less a fairy tale with each new entry. The idea that evil will always return is sophisticated and nuanced (perhaps too much so for some viewers, which is why they ditched it in TROS), and the message that there will always be good to face that evil is anything but nihilistic. It’s the very heart of what Star Wars is - never ending hope in the face of potential despair.
It’s nihilistic, because it’s become cyclical, fighting the same evil over and over with diminished returns. Ben’s redemption works, because he is a great actor, but it’s also less impactful than Vader’s redemption, because we have seen it all before. Same goes for Palpatine’s death. Aside from being a very poorly set up character in this trilogy, it was very unlikely they could top the character’s death in ROTJ, and surprise, surprise it’s spectacular visually, but emotionally vapid, another deja vu in a trilogy filled with them. I mean how many times can the destruction of the rebel fleet be used as leverage against our hero? How many Death Stars can you introduce? They’re on ships now. How original…too bad they don’t really affect the plot. What’s the next step, blasters with Death Star tech? It’s become a parody of itself.
There’s nothing wrong with introducing new threads, and new challenges for characters old and new, that expand the universe, and the lore of the Star Wars universe, just look at the Mandalorian. It is very telling that the ultimate fate of one of the characters at the end of the season is so much more emotionally impactful than for any of the characters in the ST. Aside from better writing (imo), the fact that the Mandalorian isn’t just recycling story beats from Star Wars’ greatest hits is, what makes its story and character developments surprising, and impactful, and what makes this series fairly univerally loved.