While I agree that when something is created with the intent to be used, then it should be judged based on how well it serves it’s intended function. However, ceramics that were never intended to be used for anything other than their own aesthetic merits have a different function, and ought to be judged differently imho.
Maybe it would help to think of those pieces as physical manifestations of philosophical questions the artist is tying to answer through artistic experimentation. For example, they may be trying to determine what the boundary of what a bowl is, and when it becomes a plate, and so will push the limits of that form to get a better understanding of how that works. Another example might have to do with color and mood and whereby the artist is trying to see the effects of various colors on how an object might be able to elicit a physical response in the observer. At least that’s how I try to understand why people make objects that are otherwise completely useless.