@starch12313 it's about authorial intent.
Onee san who keeps a high school boy is trying to a quick, simple gag series, and it succeeds. Aim low, hit low, forgivable. It does not pretend to be something it is not. It did not start off as a high drama and then become a gag series, just consistent all the way through.
1-nen A-gumi no Monster is trying to be a psychological drama/horror, but instead it's become a convoluted soap opera mess. Aim high, hit low. It had a promising start, but it became clear that the author had no real plan for the series, and it's consistently gotten further and further from the mark until it is unforgivable.