@Zar:
All these manga that hit bottom quickly make me curious… is there any manga that's managed to recover from that?
Dragonball pretty famously wasn't doing great in its first arc. It was introducing Krillin and the tournament that saved it.
Jojo's Bizarre Adventure radically reinvented itself every few years. Look at stands appearing in part 3 completely replacing the previous system and that was clearly something intended to re-energize the franchise and it worked, Part 3 was the part of Jojo everyone recognized and knew before the recent anime came along..
Yugioh originally wasn't about card games. The monster dueling cards was just a single one-off story around ten chapters in that introduced new rival Kaiba (the usual "desperate turn around" spot) then it had another 10 or so chapters of random games before bringing back capsule monsters as a regular feature, and then around chapter 60 committed to card games full time which is where the anime starts, mostly condensing or ignoring the first few volumes.
You can look at the radical shift both YuYuHakusho and Bleach went through after their first bit of time and figure they were on the chopping block for a while until they changed directions to full battle mangas. Their animes didn't even adapt their earliest one off ghost stories either.
Urusei Yatsura had some of that as well. You'd think Lum was the main character but she was actually only in the first chapter, and then it was random one offs for a decent while before she returned and became the lead.
Those are all much older examples and I obviously don't have actual numbers, but you can see how they started and then made sharp turns, and their legacies and eventual longevity speak for them.
Cinder