I think this is a great example of something that is different for an exceptional developer as opposed to an average one.

A developer like Carmack and likely the teams he works with are able to keep a much larger system in their head at one time than an average developer.

And this is typically why they can write larger functions like that and get away with it.

A less talented developer will be much more likely to introduce bugs near the top of that function over time as they struggle to maintain the entire function in there head.

Sometimes choosing the correct tool has more to do with the craftsman than the craft.