While there's no real way to make the concept of going back to an abusive girlfriend work, it might have been a little more palatable if the story had taken the time to show that Serina did, in fact, miss Kanon (apart from the crying after running away, which could be interpreted any number of ways), such as by showing her talking with "Aoi" about Kanon and actually talking about happier times. As it stands now, Kanon's just the woman who threw the remote control at her girlfriend for no reason, and nothing in the story helps with that extremely negative first impression.
I don't think this story was supposed to be palatable. We are supposed to have a negative impression of Kanon, she's a terrible person, an abuser who won't stop until Serina escapes or one of them dies.
To add on to it would indeed be better to not dig into Kanon's side of the story as that can be rather difficult, or even near impossible to truly portray the mentality of the abuser (Kanon) to the audience, without alienating us from the story. Mainly due to how she thinks on a fundamentally different way (in terms of how she would treat her partner) from us. Well that is if the author is someone who has had experience being the abuser and is made self-aware about it, which let's hope that is never the case.
Also it is important to note that we are looking at it from the perspective of Serina, where she is the main focus, not Kanon. Thus everything we are looking at is all the interpretations that Serina has towards Kanon, not Kanon herself.