The entire argument is one of Relativism, there is a whole lot of disciplines where there is a huge subjective element, consider journalism and literature in general, but that doesn't mean we can not have a conversation about quality of work in these fields.

Software is no different. So when someone claims that "you can't question the quality of AI output because quality of software is [partly] subjective", they're appealing to subjectivism. This position is generally held by the incompetent to entirely dismiss any question of craftsmanship or quality.