Primitive now but in their time they were groundbreaking and incredibly difficult to make work on the primitive hardware of the time and he kept pushing the envelope for a long time. Carmack is a bit of a genius, but that doesn’t mean he’s right about AGI. My own take is that actual General Intelligence may rely on any physical phenomenon from the macro to quantum effects including aspects of reality we don’t know about yet. It’s really hard to simulate things when you don’t know they’re involved. We won’t know until we try so I guess we’ll see what happens.

This is generally how science works. 99% evolution in small incremental advancements, 1% revolution in a stroke of genius that opens up new areas of science.