It's been a while since I've watched it, but I think you should take MVP to mean "what's the smallest game I can build to tell whether it is fun" and not "what is the smallest thing I can build that people will buy".
You are correct that the purpose of the MVP (Minimum Viable Product) is to test if the idea is viable. As you point out you can generally assess the viability of a product long before you have a compelling product (Minimum Compelling Product = MCP)
Making Your First Game: Minimum Viable Product - Scope Small, Start Right - Extra Credits https://www.youtube.com/watch?v=UvCri1tqIxQ
It's been a while since I've watched it, but I think you should take MVP to mean "what's the smallest game I can build to tell whether it is fun" and not "what is the smallest thing I can build that people will buy".