There are mainly two types of readers from what i can tell: Weekly or by volume. Personally, I can't keep up with Act-Age or samurai 8 weekly. There's a lot going on. So I save up a couple chapters and then read em all at once, its much more enjoyable. Therefore, I think its unfair to compare samurai 8's start to the Big dogs in the magazine. Series like kimetsu and Dr. stone are fun to read in short burst, with little gags and funny faces here and there. The dialogue is much simpler in comparison as well. They are high action from the start with simple quirky characters. Zenitsu's the scardy cat, Taiju's the strong one. Yes, there is more depth to them, but it's given later on. In samurai 8's case, the characters are much more realistic from the start.
Since kishimoto only has to focus on the writing, i don't think its far out there to assume he already has the whole story planned out. Character progression, story beats, etc. Especially since the first couple weeks we got a lot of world building and fundamentals explained.
Basically what i'm trying to say is that even though kishimoto's a big name author, it doesn't mean his series is going to kick off running (sales wise or storywise). Its a bit out of the standard, kinda like act-age. Most people read jump for high octane comedic adventures, and samurai 8 stepped out the gate with a prologue. Not saying whether its good or bad, or that it gets a pass for BEING good or bad. It just needs to find its audience and get rolling with the plot.
btw someone said earlier they wish Act-Age was higher in the ToC. But idk about that. The ToC doesn't reflect how well series is doing in jump so it shouldn't really matter. Its just formatted to be most enjoyable for the reader. So like, one piece is always at the top because a lot of people buy jump FOR one piece, or at the very least keep up with it. HxH is super popular, but it comes out so infrequently that the main demographic won't see it in jump anyway (of course some people read it there, but it started in 1998. Most of those readers aren't grabbing jump for the latest chapter of Beast children or some shit) . Nakano can just slide it in the middle and wait later for the success of the volume sales. Going back to Act-Age, it'll stay in the magazine since it can bring a new demographic to jump and it does good with manga sales. But it surely wont be prioritized in the magazine till more people vote it in the Surveys.
(btw idk if this is actually how it works. Just pieced together what the mangakas and editors have said in the passed. Makes sense in my head).