Do you know your type? How much of his music have you listened to?
If he's isfp, what's his etype? He mentions in the Tavis interview that he thinks of music as his full-time job. Workworkwork. How did you learn to play guitar so well, Prince? Oh, I was really terrible, then decided one night that all I was going to do was practice (not directly quoting because I have breakfast to eat), which is why I'm so good now. Could easily be words from a 5's mouth, but where do you surmise where his raw energy and persistence comes from? Which triad? How about a 4? 8?
So yeah, I'm sticking with sx/sp e12 infj. Perfectionist, easily expresses his ideals (which may or may not be of the fanatic sort), and maybe above all, active in everything.
Refer to that body of work.
Could it be that you're simply associating the word "artist" with words used in whichever mbti articles you've read on isfps? Curious.