I actually think by far Disney's biggest mistake with Solo was not doing the December release thing. They have so much less competition in December, and having it just 5 months after TLJ I think made people very blase towards it. I heard a lot of "oh, another Star Wars movie already?" Once they moved Episode IX to a December 2019 release date, they should've moved Solo to this December. They would've had longer to get in front of all the bad press about it, and would've had less of a problem with Star Wars fatigue. It still might not have been the hit that the others were, but I'm sure it would've done a lot better.
BTW, I don't think this is a spoiler, but did anyone else catch the throwaway reference to Black Spire Outpost in Solo? The movie was pretty hit-you-over-the-head with some of the references to other movies, but I kind of got a kick out of that reference considering most folks wouldn't get it.