This is largely a Romantic conception of art (circa early 19th century) and not one that would necessarily be true when art meant something like craft, which was what it meant for a long, long time (see the Latin ars or Greek techne.)

Medieval European artists, for example, likely would have no issue with any sort of copying or “fakes”, as the primary goal wasn’t self-expression.

While that may be true, it doesnt change how art is valued today, and its cultural position today. It's no secret also that the rough pareto distribution of art is as alive as it is elsewhere. Most art or music isnt even consumed by anyone outside of the author, conversely about 5% gets 95% of the attention, with individual pieces generating millions (and getting millions of views), same applying to music