I think you're underselling the challenge in the parts of the business that aren't coding. Which is exactly why this guy's decision is such a bad one.

He's basically said "I have skill set X, which I'm trained in and have been honing for years. For my company, I need skill sets X and Y. So I'll do Y and find someone else to do X."

No matter what X and Y are, that's just the wrong way to solve that problem. The key issue in this case being that he is assuming the marketing/user acquisition stuff is so easy that he can just pick it up on the fly with no prior experience.