I'm not sure I agree... While it's certainly true that to create the same thing that Carmack did would be a lot easier today. Working on Carmack level code remains very difficult to this day. It's just that the bar has moved.

Sure, a simple ray-caster isn't going to need a lot of optimization today. But when you are dealing with the sort of data that is now common. Optimization can be just as important.

While languages have have improved for the better, other things have created other challenges. Consider the PS3 Cell architecture. Considered to be a much more difficult architecture to program for than the processors of Doom's day.