Is Disney not understanding how badly The last jedi, etc damaged the brand? are, we underestimating how powerful the December slot is, and family movies over xmas?
I think what you are overestimating is the importance the masses give to the impact TLJ had on the Star Wars brand.
It did some damage, for sure. Lots of adult fans that used to buy all the toys and merch for every movie are now buying less or none.
But for the kids, the merch is still working, though the effect is diminished because back then Star Wars was the coolest toys ever but nowadays tons of toys exist to compete with it so it's not as important to kids.
I showed my 9 year old the old trilogy and TFA. Can you guess which one he likes best? Well, he prefered TESB because he fuckin loves AT-ATs but still, he really really liked TFA because it was flashy and action-y and faster-paced.
Kids like things that go pew-pew and ka-boom and most normal parents will bring their kids to see the new Star Wars movie, or just people that like to see visual spectacles on screen but aren't nitpicky about story quality or respect to the lore and whatnot.
You gotta keep in mind this place here is a nest of nipicky neckbeards that play MMOs all day, we aren't exactly the target audience for this kind of mass produced corporate-made movie. But despite that, most people here will still see it.
There's people like me that still enjoy Star Wars because of how much I loved it as a kid and can take the new movies with a huge pinch of salt, and just select a few cool elements from them (or the prequels) without burning the franchise as a whole because I try to be reasonable.
There's people that love Star Wars no matter what and will fanboy it to the end and will see this shitfest 9 times at the theater.
And there's the jaded angry fucks that will pay for it just so they can make a vlog about it to their 3 followers and say how much Disney/Kennedy/JarJar/Lucas fucked this all up.
Mickey is gonna laugh all the way to the bank.