Unfortunate axe. I am honestly not surprised by all the people disliking this, whenever a character is not instantly likeable this sort of thing happens, same was with Re:Zero's protag at first.
If I were to give my (non valuable) opinion on this, no, the pacing was not too slow like some say. Haven't actually seen anyone mentioning what I think would be the issue: planning ahead and structuring things properly.
The idea itself was really promising imo, could have easily been the next Kaguya. But alas, I feel like Aka had a lot of trouble deciding where to go with it at some points. It didn't really have a well structured story. And that's a shame cause, at least to me, it seems fairly easy to do:
Could have had it split on arcs/parts, with the first focusing MORE on the part where Seki and Mari were getting Kon and Pon's help, perhaps with a twist at the end that Mari was being fake as well, not just Seki. Then a focus on Kon and Pon and PROPERLY introducing/keeping around more characters than just the main 4 (like the manga club and Seki's friends, maybe even some stuff for Mari like her classmates?). And finally all 4 hanging out as a group like they started doing. Also a shame that Aka ended up dropping the whole "random love-related info" that he wrote every now and then in the chapters, feel like it was a little thing contributing to keeping the theme and making it stand out a lil more.
Well, I still enjoyed it for what it was, was always looking forward to the next chapter and genuinely liked some of the characters. I do hope Aka tries again with a different idea, the guy clearly prefers romcom stories.