There was also the severe SW brand damage from Last Jedi to consider. Writer John Kasdan openly wondered if Solo might have done better if released in December 2018 instead of May 2018:
The first eight minutes of the vid cover this and conclude it wouldn't have helped much, and I agree. Moving the release date would only "solve" non-credible problems such as Star Wars fatigue and proximity to other blockbusters, which get mentioned a lot but (for some reason) didn't affect Marvel or Fox during the same time period, only Lucasfilm.
Although Disney would have had an extra half-year to make efforts to restore the fans' confidence in the brand, that's assuming they would even bother to try (spoiler: they didn't, and made things worse instead). The real question that should haunt Kasdan is how Solo would have fared if released to a still-overwhelmingly-trusting fandom in, say, May of
2017.