For real, the way Nak treats Phantom Seer and Roboco is completely unfair
Roboco gets a small growth from big marketing (a video starring Roboco got 2 million views, but the volume only manages to sell 2k more first week...) and puts it in 3rd place, meanwhile Phantom Seer shows strong growth with almost no marketing (only one color page that was months ago), but Nak still doesn't give it any push and puts it in the back of the TOC
The only reasoning I can see behind this is "this series succeeds without marketing, so we don't need to push it, let's put it in the back", but this reasoning is just stupid...
I think there are still a lot of people here, who wrongly assume that Jump has the same expectations for manga of different genre.
Roboco is a gag manga, so it isn't even expected to sell well. The main purpose of gag manga is to draw in readers who buy the magazine, not to sell a high amount of volumes. Plus, Roboco's core audience is almost certainly a lot younger, probably even elementary school kids or junior high school students. Thus they are a lot more likely to vote in the weekly polls and less likely to buy volumes.
This means it's going to get high places on the ToC a lot more, but the sales increases per volume are lower. Also, 2 Million views on a video about a new gag manga in Jump will probably draw in a ton of new readers for the magazine, but not necessarily people buying the volumes.
Phantom Seer on the other hand is more aimed to the audience that also reads Kimetsu no Yaiba or Jujutsu Kaisen, because they're similar in genre. So it has higher sales expectations because the genre is incredibly popular. Now, this doesn't explain the low ToC rankings. But I have the theory that Phantom Seer most likely profits from the huge interest in Kimetsu no Yaiba and Jujutsu Kaisen. Both of those series have a lot of readers that only buy the volumes and don't read the chapters weekly in the magazine.
So my guess is that a chunk of those readers are now buying Phantom Seer volumes, because it is a new Jump manga from the same genre and there's some buzz around it. But since most of them are not reading it weekly in Jump, they're not going to vote in the polls for it. Thus, it is placed on the lower end of the ToC.
Basically, you can't compare the both of them. Roboco's core audience reads the chapters weekly in Jump, increasing the overall magazine sales, while a huge part of Phantom Seer's core audience seems to only buy the volumes instead of reading it weekly.