The issue with intelligence is the difficulty in actually meaningfully quantifying it.

I would say all musicians obviously have to be decently intelligent in some areas in order to do what they do, whether they play an instrument, write their music, or even just navigating the industry.

It's also really hard to tell if someone is intelligent from their music. Do thoughtful lyrics make a song intelligent? What if there are thoughtful lyrics but the composition is simple? See what I mean?

I think that's why so many people are coming up with Brian May. He has an obvious thing to point to outside of his music. He's an easy answer.

To answer your question, everyone and no one... But also everyone.