I wouldn't say it's pedantry. Art is emotional expression in an outward, tangible form. The content of this form, while varying by the creator or initiator of this emotional expression, is allocated by the physiological effect said expression causes on the viewers/consumers of it. An example off the top of my head would be film. While there really are no written rules to how a director or cinematographer should go about their art, certain things are done to cause certain affects, and this is done knowingly by the director, with these effects in mind. Like when in scary movies, you have offscreen action that turns into on screen action quickly for a jump scare. In war movies, it's typical to see a continuous shot of the main character walking through the war zone, because it creates the effect of chaos. In western films you get many extreme long shots and long shots to get the sense of openness and lawlessness. Action films you have many close ups, so you can see the characters emotions. The reason why this isn't just pedantry and subjectivism is because these are natural reactions to visual cues, there isn't a set of rules, and it's not nit picking, it's simply knowing how artistic expression will be received due to how our brains work. I can think of more examples, I'm just writing an essay on a film right now, so these ideas are still fresh in my mind.