That's only valid if the existing co-founder is capable of (literally) pulling the entire company product out of his ass, if he needs to. If he feels he's not capable of it, then he needs to adapt to the person who is capable of writing the entire product by themselves in their technology of choice - because that's the kind of person you want as a technology co-founder.

As I said, early employees are a different matter. They need to be shaped around - well, around the technology co-founder who wrote the whole product in a storm of caffeine fuelled fury.