The issue can be summed up under the sentence "the author is not very good at handling tonal shifts." Mikanuji also is basically making up drama and new characters as she goes along. This was what, originally an online thing that can end at anytime, but then it got picked up to be serialized. Where you can longer play that fast and loose with plot. Got to have a direction of some sort. Except we don't know if it's heading for the cliff or somewhere sensible.
I think the issue is more succinctly summed up as “if you read subtext into a story where there is none and it diminishes your enjoyment of it, that is not a failing of the author”.
For example, if you read Moby Dick and focus on how Melville’s portrayal of the disabled reveals his ablist agenda and due to this tonedeafness you hate the story - well, that’s okay I guess.
Fusoroi has a lot of faults, but an ultra-realistic representation of human relationships it is not.