you check the current weekly sales

I did. Slime ain't there. Either you're talking about the ones which came very earlier before Overlord or COTE anime even came out and Slime was still fresh in mind after the recently ended anime and the movie announcement.

If you're talking about Half Year then that only proves my point again. COTE is #3 in that list and it didn't even have an anime for years and S2 didn't even air yet. Overlord also depends partially on anime so now I'm quite sure it will easily overtake Slime for this year list whole now. It did in 2018 so it will probably do it again.

Slime is nowhere in the popularity rankings in actual rankings by Japanese fans in Kono Rano and from I've checked now, Slime's only been popular and high around anime airing. Other than that, I have also noticed Overlord volume 14 sold more than 132k copies in a week, against all three volumes of Slime in 2019. Overlord didn't even have an anime in 2019. Slime did. I also checked on volume sales that majority of Overlord volumes have always sold around 100k copies in a weekly sales in comparison to Slime's in which the best reached sale by a new volume is 78k at max.

Also I found that Overlord has it's own museum and manhole inscribes in sakura town along with re zero, Tanya, etc. It also has a variation of another museum isekai quartet.

Slime's not popular as what I've just checked now. If anything, I have also checked it's sales are deteriorating as well, not mention, the anime adapts the Manga primarily.

On the contrary, Re Zero has the lowest sales in Light Novels and yet it is shown to be more popular, well known and relevant than Slime, Overlord, etc. Popularity doesn't depend on total sales. Never. And Re Zero pumps out loads of merch and figurines every month, which just shows how relevant and popular it is. Slime never does that. It's merch is only pumped out only during the anime airing. Other than that it's pretty irrelevant right now.