mapping can be considered an art form yes
that doesnt mean quality doesnt exist though lol, "there's no such thing as a bad map" is a cruel lie to tell yourself
every artistic/creative field has a bunch of theory that attempts to explain how that art form works and how to make good pieces of art. mapping is no exception. conventional mapping theory uses a lot of concepts from visual art and graphic design to guide the visual design of a beatmap. we also use our understanding of how the game is played to represent the song through gameplay and to make a cool experience for our target player audience. there are a lot of things that can be done well or poorly depending on your level of understanding and skill.
so, rather than overthinking, you're just underestimating the depth of both art and mapping.