There are some sci-fi that are written as novels, but there are some that are written as "alternate future". Much like Black Mirror they imagine a particular technology or event, and attempt to extrapolate what would happen to society based on that. When telling a horror/dystopian story, short-form works fine as there are any number of ways things can go wrong. When telling a hopeful story, as many of the alternate future works try to be, more time has to be spent on how the pitfalls of dystopia were avoided, the struggles and horrors overcame, etc. I think of Foundation as a parallel to the alternate history books, where they imagine something like, "What if Napoleon never invaded Russia?" and extrapolate from there. Such a story can't be told over one person's lifetime in any meaningful way, the effects are too far-reaching. I don't think anyone who is truly honest with themselves will disagree that portions of Foundation are boring. But Foundation isn't remarkable for the pacing or prose, but for the ideas it introduces and the scope of it's narrative. Comparing to Jules Verne or H.G. Wells is fairly appropriate, as they all were enthralled by the possibilities of human ingenuity and dazzled by the brightness of the future they saw. It's true the older writers wrote better stories, but that doesn't take away from the ambition Asimov had to try to share his vision entire. Doubtless if Wells had written further novels to explore how humans became the Eloi and Morlocks as well as what happened to the nations of his day, or even what else was happening elsewhere in that future time, portions of that would have dragged a bit as well.