If you assume the technical co-founder doesn't need to sleep or has a magical source of extra time, sure. But in the real world, failing to bring a product or service to market at the appropriate time can be the difference between failure and success. I certainly agree that a technical co-founder's knowledge is harder to replicate in the abstract (OP's story about a co-founder suggesting an 80:20 split is nuts) but trying to be a jack of all trades can leave you a master of none.