Yeah, hello indeed! To be honest, the idea of Mark having extraordinary skills thanks to how his brain is wired is a little bit far-fetched. John Mayer is as right-handed as it gets, and yet he can do the same stuff, amplified to 11. His famous song "Neon" is a nightmare even to play on a guitar alone, but he sings it and plays it at the same time perfectly.
Playing and singing at the same time is not magic and is something musicians have done since ancient times. It's practice, practice, practice, and practice.
It's known that a lot of creative people are left-handed, and when I was a kid, I thought that was why I was not creative, but I found out it was just an excuse for me not to work. Again, there are tons of examples of extremely talented, skilful or successful people who are not left-handed or blue-eyed. Talent and work are the only things that matter.