Indeed it's as if we've harvested all the large oak trees and can no longer make trans-Atlantic wooden ships and now must move on to metal. And doing that actually required stumbling on coal which ultimately was old wood. And then metal enabled us to move past coal. None of this was necessarily visible at the time but is the arc of progress. Of course mathematics being a purely abstract thought medium may not have the benefit of the physical / material world's progression. However it is ironic that here mathematics is progressing specifically because of how far along our material world has come. We're already at the point where a tiny nearly nil percentage of the population can reason at the frontier in mathematics, Terrence Tao obviously included in that small number, and if in the future that number truly reaches nil and only computers can go forward it's not so clear how fundamentally different the world will be to me. The hope is that the innovative manifestations in the real world will be able to be enjoyed by all just as one hopes mathematicians' thought exercises do unlock real blapplications.

I think the deeper point Terrence is making is simply that the information revolution which is the culmination of the mathematics revolution has less low-hanging fruit today. That was true ever since Claude Shannon