Now we are definitely getting into the Star Wars fatigue area because they are only content with having movies that are still connected to the mainline movies that we've known about for 40 years now with two side movies thrown in with stories we know already that no one asked for.
I don't think the number of movies necessarily matters. A good example of this would be Marvel where we've been getting at least one Marvel movie every year for the past 10 years... and that's just counting the ones directly from Marvel Studios. Although, what probably does help is that sequels are generally not created in tandem. They create other stories in between to give us a break from what we know before returning to it. Marvel give us
at least two years between a sequel, and in some cases, it's about 3-4. (Thor The Dark World to Thor Ragnarok is the longest at about 4 years.)
Now, there are some differences here. The biggest difference is that Marvel movies are fairly self-contained stories... with the exception of Infinity War. I think Episode VIII has elements of that, but it's still a direct continuation of Episode VII. This is incredibly awkward when you use a different director who creates a continuation that arguably "feels different" than what came before it. Marvel's self-contained style allows them to create movies that are in the same universe/timeline yet they can feel completely different. A good example is the staunch difference in tone between Thor The Dark World and Thor Ragnarok. Arguably, that difference in tone isn't
too much different from what we saw in Episode VII versus Episode VIII where the latter tried to be a bit "funnier". (Although, I did watch a good video earlier detailing how Episode VIII's funny bits actually worked against it as they tended to deescalate the tension.)
Now, what's wrong with Solo? Eh... honestly, even ignoring it as a Star Wars movie... it's just not a good movie.