Does it have to be that way in a trilogy just because Empire went that way? I mean, BTTF 2 (arguably one of the best sequels outside of Empire) ends up with things pretty well tied up in terms of bad guys, but Doc being stuck in the Old West. I think this will play out a lot more like BTTF 2-3 than Empire-Return. Granted, neither of those final installments are all that fondly remembered
But what I mean is I think it's setting up for a lot less of more Empire-Rebel retread, but probably a conclusion of the very personal conflicts of Ben Solo. This movie proved that it believes a rebellion, resistance, whatever you want to call it is more than a single person. I'm sure Ben will face consequences of his massive failure at the end of TLJ. So I think it's more of a continuation of a story like 2-3 was than how Empire-Return were very strict and traditional parts of a 3 Act narrative. Different? Sure. Bad? Nope.
And this isn't a response to you per se, but Star Wars isn't mine. It isn't yours. It isn't anyone's. Nobody has ruined Star Wars, because it's not a thing that can be ruined. The legacy will live on in so many different ways, that people need calm the hell down with the "ruined, trashed, destroyed, disrespected" over the top nonsense narrative that's being thrown around right now. It's all just 2017 over reaction culture. Yes you can indiviually be disappointed, but just beause they didn't tell the story you wanted to see doesn't mean it's a bad movie