@Nick86 I don't think the medium has anything to do with the things that were skipped. The manga has skipped almost all of the parts of the story so far that were from the perspective of other characters later in the timeline(the other reincarnated students and the teacher as they grow older), and then suddenly they don't skip the demon war meeting.
Also, I don't get what you mean for Slime. Do you mean that the story isn't good? If so I disagree, it's no masterpiece, but it's still quite good and LN volume 5 was great. Also, the manga is a very good adaptation, one of the best I've seen, and I love the art in the manga.
If you mean that the side stories aren't good, then I agree that they are sub-par(but I'll still read them). However, while asking for there to be side stories of "Kumo Desu ga, Nani ka?" isn't something I'd disagree with, I do think that it'd be better for the manga adaptation of the main story to start adapting the parts of the story that were skipped already.