There is a measure of truth to what you say. Yet there are plenty of musicians, like actors and writers who will try on other coats so to speak. Some more convincing than others certainly. I've no idea to the veracity of Sting's Gaelic dabblings, and might I add,I have no appreciation of this. Derivative music, art, etc. is in part ,the shoulders of giants we stand on. I've not lived the life of a bluesman, but that doesn't stop me from trying my hand at BB King or Willie Dixon.
Children it is said will repeat words and phrases on the average of 76 times in the effort to learn them. More than one composer has stated, "I don't borrow, I steal with both hands".
In a funny paradox -and this may be arguable, Sting used the Police as a vehicle to reach a point where he could play jazz instead, and would be heard. And lastly we've heard the Stones ripping off country/blues/folk and making it their own.By any means necessary, imitation, theft or mimicking it can all work