I think what he meant was that the current benchmarks are unable to quantify the benefit to users of having a GPU for computational power while the other is driving the displays. The new Pro configuration suggests you'll be working in real-time when doing graphically intensive tasks rather than waiting for something to render. Animators & video editors will benefit from this in ways that are difficult to slap a technical benchmark on.

These machines are probably aiming to scoop up some high-margin high-end workstation business, hence the demo by Pixar at the last WWDC.