Rian is actually a good writer. Had he handled all three there would have been internal consistency amongst ‘his’ trilogy at least.
Here's the thing, I think he displayed very little creativity with TLJ. I don't think he has the creativity for Star Wars. There's more interesting new stuff in JJ's films, than in RJs.
TLJ is, "The Resistance needs to escape. They escaped. No, they didn't. They need to escape again. What's the plan? Here's a plan. It didn't work. Here's the real plan. It's not working. The Rebels now need to escape and they escape."
When TESB did this escaping plot, it was way more interesting, with asteroid fields etc. Not, "we're low on gas."
Rey's plot is a truncated version fo Luke's from TESB and ROTJ. Minus the most interesting parts. It's stripped-down, simplified and relies on you knowing the beats. The young jedi student goes to the mentor, has a connection to the bad guy, wants to redeem them. Something something throne room scene." It's subversion is only there because it's retelling the same story. Rey only wants to redeem Kylo because that's what the young Jedi does in Star Wars.
Key to understanding TLJ is knowing that it's broken down elements of the plot to the premise of the original trilogy. TFA may have been a soft remake in big ideas, TLJ literally approaches it as if it's telling the exact same story, but simplified. Then goes, "oh you thought that was going to happen, well it didn't."
This is why Luke sucks in that film. RJ wasn't writing Luke Skywalker, he was writing the mentor roles in his slightly different retelling. Apparently this appealed to film critics, who fell for this lazy writing. Which speaks more to how little they think of Star Wars than anything else.
Got a character Poe, well let's make his story about how roguish male heroes, who break the rules aren't always correct. His plot can be exploring his stereotypical character.
Finn, well he's something new for Star Wars, no analogue in the original. Nothing for him to do. Let's just use his plot to waste time and preach about animal rights, dangers of capitalism and that both good guys and bad guys buy ammo.
Leia, no analogue for her in the originals. Ironic. Put her in a coma!
Galaxy being conquered, Put it in the opening crawl.
Where does he end the film? Well he's stripped it back even further to the most basic premise of the original trilogy. Now with less plot lines. There's a young Jedi. An evil empire that rules the galaxy and a small group of rebels.