Here's where I have a problem comparing Star Wars box office performance with Avengers (and, for that matter, Harry Potter.)
Avengers and Potter were completed in a much shorter time frame with consistent casting and a consistent audience.
You don't think if 7,8,9 were completed with Han, Leia, and Luke as the main characters (in their prime, preferably 20 years ago) that box office numbers would have blown away expectations? Of course 9 would have delivered better results than what we are seeing now - no matter who wrote or directed it, frankly.
The reason Star Wars (an original franchise, btw) exists as a cultural phenomenon (which Avengers are not, IMO, they're just popular movies) is because of 4,5,6. Had they started with Ep 1. at the time Ep 1. came out, it would have been nowhere near as big a deal.
There was a crazy time lapse between 6 and 1. Fans had to start over with a completely new cast. Then they had to start over again with a completely new cast in 7. You will never be as invested in Rey in Ep 9 as you are in Hermione in the last Potter movie. There's no way. You grew up with Hermione over all the films in the natural course of the life of the actress, and in some cases, as audience members of the same age grew up alongside her.
The big three in the Star Wars universe had effectively bit parts in the last three movies. (Yes, Luke was pivotal, but had precious little screen time over 3 films.) That will always be Lucas' fault for waiting so long to do the prequels, and then doing the prequels before the sequels, knowing his cast was aging out (and I'm guessing some of that is on Harrison Ford for not wanting to be involved. OK, Harrison in the 90's: you want to do another Indy? Sign a contract for SW ep 7 right after.)
So the reality is you have 3 distinctly separate trilogies, tied together by a storyline but not by a cast. I am maybe just now ready for Rey, Poe, and Finn to carry their own movie, but they're over, too. Down with the Skywalker ship (and from what I understand some of them didn't want to do more, either.)
The Palpatine thread retroactively tied all nine together. That was clever. I enjoyed the sequels much more than the prequels. I had no big issues with TLJ, and I very much enjoyed Ep 9. But the reality is "Star Wars" is 4,5,6 for me. And I think Lucas was getting a little blowback after RoTJ (there was chatter about the Ewoks at the time almost like there was about Jar Jar Binks.) So maybe he thought he should quit while he was ahead, and didn't see a way forward to a successful 7 right then (although we all know he wanted to do 9 installments going way back to the early 80's at least.)
It was bungled. Not by Disney.