One thing to possibly consider is that Samurai 8 may actually have less potential for huge growth than a newbie author, if it starts off low.
With a new creator people won't instantly have faith in what they're doing, people aren't going to just pick up this random newbie's manga because of the cover, I imagine a lot will probably wait until it's already popular and widely talked about then jump on. WSJ is famous for it's harsh expectations after all, there's no point wasting your money on something by some unknown creator that might just get cancelled as soon as you get into it.
With Samurai 8 however everyone already knows Kishi, Naruto fans who don't read wsj will probably all have heard of it already, and people who are just browsing in-store will see the promotion on the stands and know who its by. You won't get as many people who were unsure at first jumping into this new series later after it becomes a stable hit like with Kimetsu, Jujutsu, etc.
Considering the current state of Jump it'll probably last 7-10 volumes anyway but if something by Kishimoto, the Naruto guy, can't sell impressively first volume, despite all the promotion, then I can't see it growing too much later either. If buyers don't care about vol 1 and 2 it's probably not too likely they'll care about later releases either.
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