I believe there's a baseline "mediocre", but something can be baseline mediocre and be subjectively dry, boring, and uninteresting. That being said:

Art: if you are doing non-abstract figure drawing or painting, there is a knowledge or referencing of anatomy, foreshortening, and perspective that should be implemented in the work. How much stylization is up to the artist, but clearly misdrawn fingers and toes and poorly built figures (we see you, Rob Liefeld) in otherwise quasi-realistic renderings shouldn't be excused as stylization.

Music: music is based on frequencies and math sequencing. There are notes and chords that sound good together, and notes/chords that do not. Singing off-key is still a thing (the note doesn't change b/c you can't reach it, TRUSt ME I KNOW), even though if you have enough subjective style that is appealing (see also: Mary J Blige *ducks*), you may be able to pull it off.

Film: presuming we're talking about studio films, there are certain professional standards to writing (the three act structure), direction (how the acting, shots, etc fit the narrative0< cinematography, lighting, editing, sound, and special effects that are necessary for a film to look professional. Some of these (particularly the lighting, camerawork, and sound) I consider non-negotiables: simply making sure that images and sounds reproduce properly on film. If these things aren't in place, it's hard to get your film to even a subjective mediocrity.