Intelligence isn't a spectrum, it's an infinite-dimensional space. Someone can be smart on one axis and a dunce on infinity-minus-one other axes. Every genius ever born was almost certainly mediocre at nearly everything outside their expertise.
And even today such people exist. Encountering them is often quite an experience. Seeing them being better than you at almost everything is on one hand really nice, on the other hand it makes you wonder what you did wrong. Such folks are usually quite rare though, 1 in a thousand types of people. But I'd imagine Google should be full of them. Or maybe it isn't, idk, given GP.
Without any examples of his work it’s hard to believe that they are of any consequence. I don’t think anyone can just write a piece of music, but you don’t present a strong case that anything he wrote is even remotely worthwhile.
Hell, Bruce Willis has a band that’s released records. I just don’t see any reason to think they’re worth listening to over anyone else.
Form Wikipedia:
> an individual's performance on one type of cognitive task tends to be comparable to that person's performance on other kinds of cognitive tasks.