"ZBook Studio. Clearly competing against Dell's Precision 5520 (and in nearly all ways, surpassing it)"

That's not true at all, in fact, if you must compare, the 5520 is actually few steps ahead. But that doesn't matter, because there's absolutely no reason to buy these overpriced "lighteweight workstations" that don't even have ECC support or high end graphics.

There's plenty premium consumer laptops in the 1.5~2kg range, that come with 1050/1050Ti graphics that are simply better in price-performance ratio. Beginning with better known "all-around multimedia" laptops like XPS 15 or Zenbook Pro to budget gaming laptops from ODMs such as Gigabyte Phantasus, Aorus, Clevo, MSI, Asus, Eurocom, etc. That is of course, if you're willing to compromise a little of battery life and build quality.

Either way, the only major highlight for 2017 workstation laptops is the inclusion of (1070 equivalent) P5000 graphics with whopping 16GB of VRAM and VR support.

I'll never recommend Zbook Studio Model, for my experience with it was a complete nightmare: the extremely high surface temperature, suck battery life, and poor build-quality(the keyboard is even not flat!)  The screen break down twice in half a year because of the high temperature. Zbook 15/17 will be a wise choice (I'm using Zbook 17 G3 now and it's great from every aspect actually)

I am wonder when Lenovo is going to make quad-core i7 based workstation with ~2 kg weight instead of ~2.7 kg (P50)?