I think the complexity of 3 dimensional travel vs. 2 D. resulted in advanced brain development as the 3 D travel became more developed, a feedback loop situation.
It’s probably the Gray’s ability to travel in 4 dimensions
that let them survive in the future, while we become
extinct.
I’m sure you’re right, as it relates to brain development. But, when sudden climate changes occurs, having the ability to relocate, quickly…. And knowing where to go, was a big advantage. I doubt the large herbivores were highly mobile. Food sources dried up quickly.