Copyright isn't useful because it creates artificial value, it's useful because it lets a work with a high production cost be distributed for a low per-copy cost, amortising the initial costs over many consumers. Without some sort of model that allows this, we would be back in the dark ages where magnificent works were produced only by artists with rich patrons.
Copyright was created as an incentive to create. Personally I believe that if there were no copyright law, musicians would still create.
I don't think anyone would argue that in the absence of copyright, nobody would make music any more. However, that doesn't tell us whether the same quantity and/or quality of music would be made, nor, ultimately, whether the same number of people would get as much enjoyment from listening to music as they do today.
No-one is forcing musicians to rely on copyright. If production costs are so low and giving away their work for free really generates increased overall income via secondary effects, then it is remarkable how little evidence there seems to be of professional musicians choosing that alternative strategy.