I think there are several things that are going on:
1) The Last Jedi was such a horrible movie that it effectively killed the francise. The people who rushed out to see it are in a “wait-and-see” mood for Solo, and in a “skip it” for Episode IX.
2) I don’t think Solo dieing necessarily means people won’t be interested in seeing him again — but Harrison Ford was so iconic that they really needed to (and didn’t) find a really good actor to be the Young Solo.
3) Go back and rewatch the first Star Was trilogy to study Solo’s character. He is contemptuous of Leia “Your Worshipfulness” [Mysogny! Sexism!]. He is confident and capable [Toxic masculinity!]. He kisses her without getting signed¬orized written permission [#metoo!]. In short, he is a character that Hollywood will not create today, meaning that no matter how objectively good Solo is as an independent movie, it is not going to show the character Han Solo.
I liked “Solo,” and I really liked “Rogue One.” It’s the episode movies that have been disappointing.
That's a really good point.
The moment I read your Comment, I thought about the young Robert De Niro playing the young Vito Corleone.
If Disney had found someone near De Niro’s level to play Solo, they would have created a completely new film franchise for decades to come.