There are lots of less famous researchers toiling away who are also very smart and who have much more detailed specialist knowledge. I don’t doubt John Carmack’s intellectual ability, but he’s famous because he made some cool video games, not because he won the America’s Smartest Person competition. This idea that he’s the AI messiah seems almost cultish.
I believe all his in-depth experience in other areas will heavily unlock him to bring about another breakthrough. He's that good.