I haven't read Kimetsu No Yaiba, but I was (Still am) one of the users in the "Jump won't let Kimetsu end so early" bandwagon.
But what exactly does Jump consider a "climax"? The last arc? Or the last stretch of the last arc?
Because there are plenty of series where last arcs ran for like 20 volumes.. Heck, for example, I remember back when I read Dai No Daiboken in like 2005 (And I had no idea it was a 38 volume series IIRC) I kept buying the volumes every month, I think the last arc started around volume 20ish and it ended up having 38 volumes! So yeah "Climax" is such a vague word and authors can extend said climax or final arcs, that a manga can be in its "climax" for like 2-3 years lol..
Talking about the word climax, didn't Jump use that very same word (I dunno if it was literally said in Japanese or it was translated or something) but didn't they use the same wording or something similar during the whole last arc of BLEACH (I think it lasted for like 20ish volumes or something?)
So yeah.. Climax is just too vague lol, even if Kimetsu is in its last arc it could just pull a Dai No Daiboken/Naruto and extend it to like 15 volumes lol