Star Wars is way smaller than people realise. It's almost entirely about a single family and a few friends, despite the backdrop of galactic proportions. So, of course, when you try to make spin offs, the board at Disney is at odds at what they can do. They have no idea. Rogue Squadron was a kind of an exception, because they actually took the time to create a new story that could be anchored in ANH, but these guys will just do things that are too obvious, and thus boring. "Hey, we know you like the Millenium Falcon! And Solo! Let's make a new film called... ahhhh.. SOLO!" Then, they'll do this movie called KENOBI, or another movie called "I_RECOGNIZE_THIS". It's pandering to the lowest denominator. Once you see the title of the movie, you basically know you've seen it in your head.
Rogue One is a really good movie that used the franchise to tell a story that the franchise so far hasn't attempted to tell. It was also from the ground up designed to feed directly into A New Hope, from its story to its tone. It's a gritty war story in which, at the beginning, all hope is lost; everyone is rather cynical and going through the motions not because they think they can defeat the Empire, but because it's the only thing that is left for them to do. The mission they execute is a forlorn hope, a desperate last shot before the Empire actually, truly, becomes undefeatable, and it is pulled off at great cost.
When Leia says "Hope", at the end, it represents a shift in tone that leads gently from the war epic of Rogue One to the naive optimism of Luke Skywalker staring at the Suns.
Rogue One also uses its mandatory cameos from established characters really well. Darth Vader appears as a holy terror of a man, a true monster that is as unstoppable as the Death Star. Tarkin is established as a ruthless schemer and backstabber, Mon Mothma and the rest of rebel high command are established (and Bail Organa gets a sendoff) as well-meaning but kiiiiinda ineffective.
So, why was Rogue One a success and Solo was not? Leaving aside the notion of people cooling on Star Wars (which may be a factor, but not a big one imho), Rogue One had amazing trailers. There are shots in those that are immediately intriguing and beautiful (that beauty shot of a Star Destroyer in front of a starfield that, a frame later, is established as the Death Star's shadowed side was amazing). The story has a good dirty dozen vibe to it, and as mentioned above, it wasn't one we've seen the franchise try to tell yet.
Solo, on the other hand, takes the most boring story possible from its starting premise. Han Solo is a smuggler and a scoundrel from a world of smugglers and scoundrels, so what story do we tell? A heist movie.
Nothing wrong with that, of course; heist movies are popular for a reason. But then they made the mistake of banking on interest in the
characters as opposed to banking on interest in the
story or actors; the pitch wasn't "watch Han Solo deal with something he hasn't dealt with" (like, for example, life as a new father with Leia; believe it or not,
that's a movie I'd actually watch) or "watch a bunch of the highest profile actresses in cinema do a heist movie", the pitch was "See how Han Solo got his blaster and spaceship and cool yeti friend".
That, to put it mildly, is not a solid pitch to audiences. It could have been, of course: If the film had cast more high-profile actors (Danny Glover is great, yes, as is Woody Harrelson, but they are not by themselves audience draws, and if her past few appearances have told us anything, it's that Emilia Clarke isn't that great either), or given us something that seems like a n interesting story (like having Han start off somewhere not scoundrelly, for example).
That people collectively went Meh at it is really not surprising. I do not remember any point where I saw people genuinely hyped for the thing (unlike Rogue One!).
MARVEL does not suffer from this lack of material to create new movies from. All they have to decide is what movies *not* to create, because once someone says "Captain Marvel is greenlit", they all basically know what to do. In Star Wars, they have no idea. So they just rehash the same kinds of people, the same kinds of robots, the same kinds of biomes, aesthetics and so on.
Regarding aesthetics: Take a look at the leading ladies of Star Wars films so far. For some reason, they've all been petite white brunettes. Why is that, I wonder?
Production problems are nothing new for Star Wars. New Hope was marred with them too, and eventually saved in the editing phase.
A New Hope wasn't reshot almost entirely. Try again.
ANH was saved in the edit, yes. Using material that was shot on location. If you look at behind the scenes documentaries of the prequel trilogy, it becomes apparent that that's just how Lucas operates: Shoot a lot of material on stage and then find the movie in the edit. ANH was an instance of the system working as designed; Solo was an instance of the studio trying to salvage a project that, for some reason or another, stalled out.
I have already written about this: there's no good "lore" to write these new spinoff movies.
All the spinoffs can do is to reinvent the old SWEU in 120 minute intervals. That may lead to good results, like Rogue One, but it can also lead to Solos. I do not want to see the film equivalent of, say, Darksaber; every Star Wars movie takes a much greater risk than any given Marvel film as you've pointed out and so there's little room for errors of the sort that happened during Solo.