I personally doubt that Bono's having those lyric-notes stolen made much difference to October. It's a good story, but in those days Bono's approach was to sing whatever came to mind at the microphone, and he changed lyrics up to the last minute constantly. And since the incident occurred shortly before the recording sessions, you'd tend to think he pretty much knew what he was going to sing anyway, even if he might have forgotten a few good lines here or there.
I also think the "band was going through spiritual crisis" story has been a bit exaggerated over the years as a way to explain why the album was less successful (see also: "Pop would have been hugely successful if we'd had three more months").
I think the challenge with October was more to do with the band's having maximum one year between Boy and the next studio album, which has never happened again since. They got a bit more time to polish War, and with Unforgettable Fire they asked for and got more time from Island to finish it. As we all know, they switched a making records at a snail's pace in the 90s and beyond.
I think October just suffers a bit from "sophomoritis". It doesn't have the hits like War and it's not mature like what came after that. And the difference between Boy and October is that Boy is "the first U2 album". Which leaves October with nothing to excite casual fans with.