I said "X" instead of intelligence, strength, mass, reaction time, precise control, spatial awareness, or any other single characteristic because the best athletes have to be great on multiple dimensions - not just one. The same goes for "intelligence", unless it's used by Land as a catch-all phrase for multiple attributes, and if so, the statement becomes pointlessly vague, and papers over the fact that some of these attributes have physical limits and can't be changed by the self-improving intelligence, this limits are present in any medium e.g. latency, bandwidth, signal attenuation