I don't think Last Jedi had much to do with it other than proximity of release dates. Reception wise, Last Jedi was better received than Solo, even though audiences who saw it still like Solo. Last Jedi was at the top of the streaming movie charts when it came out, and is still #2 on Blu Ray sales. So aside from online fanboi's who don't like the movie because it "ruined star wars", LJ was quite popular.
Regarding Solo, there's a lot to unpack here. A lot of things went into this opening to be very lackluster.
* Only 5 months since last SW film
* Very close proximity to Infinity War and Deadpool, which have similar demographics. I have several friends who are interested in Solo, but they don't see it as on the same level as LJ or even Rogue One (in terms of the epic quality), and since they just went to the movies to see Infinity War, they may wait until it's available for streaming.
* Summer, as opposed to December: December had become "Star Wars Season" in the mind of the public consciousness. Couple that with:
* Not nearly the same level of marketing as for the last several films.
* Memorial Day Weekend has been notoriously bad for new movies for about the last 10 years. Whoever decided to release Solo this weekend must have been crazy.
Really I think the above combined for the big drop. Also, Solo is a fine move. It's a fun tomorrow, as many have described. But it's not a blockbuster level Star Wars film. Beyond the Saga films, Star Wars as a modem franchise is still trying to get it's footing. Marvel and the MCU went through the same growing pains. Hulk/Thor/Captain America, the First Avenger, and Thor Dark World were all not as well received as the Iron Man films. Yet Marvel had found their footing: most of the movies in Phase 3 have been excellent and very well received. Star Wars has to be able to experiment without fanboi's jumping around whenever they make a bold creative choice. They also have to start avoiding "safe" stories like Solo and go in more interesting creative directions. One of the things they Marvel had figured out is that the different movies have to be different types of movies, different styles, different tones, in order to be successful in the long run.