i wonder how long it takes to get a ping reply from outer space.

Yep, Carmack and Romero were like the Lennon and McCartney of the gaming world, because they were different but still had enough in common to be friends and therefore balance each other.

It's stated many times in book Masters of Doom, that Romero was always the one who was driving the engine to it's limits. He was also very necessary to kinda point Carmack to the right direction gameplay-wise. as Carmack was the master on the technical side, he was getting his fun from technical challenges and that's why he needed somebody to keep him on the right track.

When more technical people are working alone, they create piece of shit productions like Revolution 9, but when they are working with somebody that has an insight on the "other side", they are unbeatable together.