Every trade has a set of skills. Skills can be judged as to weather or not they are well used. A carpenter who can't measure is a bad carpenter, full stop. To suggest that all of these choices are merely subjective and have no basis in skill is to deny the obvious. To further suggest that we cannot judge what is good because we have not yet heard the best is to refute everything we have heard. This seems to belong to the "I don't know anything about art, but I know what I like", school of thought.
We can make informed judgements, Mozart is better than Brahms.He does more creative thigs with his skills and he understands the skills. Bonnie Raitt is a better Blues singer than Otis Rush for the same reason.
But they don't have to be perfect to be enjoyed but I still prefer Bonnie Raitt.