You are talking about magic, not abstract concepts. Abstract concepts can be defined. Claiming opposite is ridiculous. A word is meaningless if no one knows what it means.
Beauty being subjective is irrelevant, because so is a thing being considered "art" - it's subjective, no matter what shamgic it supposedly has according to it's producer.
In the end "artists" are just selling their products like everyone else - for money, attention, praise, status, good emotions, etc.