Trilogies are an excellent format for telling stories: Beginning, middle, and end. That's how stories are written.
Trilogies fail when there's no coherent, cohesive story to tell.
As I said in my post, they can work
if they are tightly planned and told in a really crisp manner. But I think the restrictions of runtimes (2-2.5hrs) don't really allow enough time for characters to develop as effectively as they could, and therefore to sell the dramatic moments. You can run through a trilogy that ticks off various plot points and which will flow neatly from A-to-B-to-C, but it'll lack a lot of the development necessary to earn character moments and it'll end up feeling rushed.
There's also something to be said for how each individual installment handles issues of pacing and providing opportunities for their characters to develop so that they can earn those moments.
Ben's redemption arc is a perfect example. (I'm not even touching on Reylo, given how massively out of left field that felt to me.) In the first film, we set up Ben as conflicted. He knows he still has a spark of good in himself, and he's trying to extinguish it. What does he do? He murders his own father. In the second film, he feels a strong connection to Rey, but also seeks to exterminate the past. The film continues his downward spiral towards evil, and ends with him arguably at the bottom of that spiral, having embraced evil and his desire to utterly destroy the past and rule the galaxy with an iron fist.
In ROS, we start out with him in this deeply evil place, but his turn back to good happens incredibly abruptly, and then he is
all in on being good again. The justification is apparently that Rey kills Kylo Ren, and resurrects Ben in the process when she heals him. So, basically, she stabs him, lays hands on him, shouts "DEMONS, BEGONE!!!" in her best hellfire-and-brimstone-preacher voice, and presto-changeo, Ben's back! Huzzah! Not only that, but he's back to kick ass for the light side
and he's all out of bubblegum.
You can tick off these points in three films. But making them feel genuinely earned is the real trick, and they don't in these films. Now, some of that is because we're busy chasing Rathtars, and going on jaunts to Canto Bight, and hyperspace skipping and going to Space Diwali, etc., etc., etc. But all of that stuff is necessary to keep the films from bogging down. They kinda need to be action-packed.
But that's just it: you really can only pick one and do it effectively. You can have an action-packed, thrilling rollercoaster ride, but you won't get a ton of great character development, and your conclusions will likely feel rushed. They'll be thrilling, but they often won't feel earned. Alternatively, you can spend the time within each film to try to earn them, but your film will start to drag or be overly long if you try to do it all in one go.
That's why I think you either need to keep the story really tight and very, very carefully balanced between plot/action and character development, or you just have to accept that a bunch of your moments aren't really gonna survive much close-up scrutiny. Or you have to abandon the trilogy format.
But what format is it. Thinking of your post, I thought about series. But there a lot of great series with bad/rushed endings. GoT as an actual example.
Young people liked the ST and I'm talking about people who can keep focused on stuff less than ten seconds. And the ST is exactly for that crows that does not think anymore and just keeps smiling about what they've seen.
I've not so many problems if something is a bit out of canon, but I really hate that miserable story telling that we're presented. And that is not an exclusive SW problem.
GoT has its own problems that I won't get into here, but yes, it suffered from rushed storytelling, too, and an over-reliance on "Rule of Cool." Most people I know were
not happy with the ending. But that show had also changed dramatically from what it started as into what it ultimately became, and suffered as a result. People went in with a particular set of expectations, and the show runners screwed them by not living up to them.
With the ST, I think...honestly, people are fine with it because they treat it all just as a big popcorn movie. And on that level, the ST basically works. Certainly ROS does. It doesn't really try to be anything more than that. It knows the audience doesn't really care that a lot of its emotional beats aren't earned within the narrative, and are more piggybacking on meta-narrative things like your own love of certain characters. It doesn't care. The film knows what audiences want, gives it to them, and invites them to just sit back and enjoy the ride.
If you go into it with that attitude, it delivers. If you want something more, something more meaningful, a better work of art....you're lookin' at the wrong movies, pal. That's not to say Star Wars can't be that, but rather that was never JJ's goal. It never is in any of his films, really.