They do not explicitly mention link power management, but I'd be surprised if they were not aware of this, since I remember this issue being mentioned in c't several times. They did ask Dell about the discrepancies in power consumption, and Dell says that it's mostly due to the new Kaby-Lake Intel GPU, which is not yet properly supported by Linux, and that probably the combination of Xorg and Unity draws more power than Windows.
They were able to reduce power consumption by 0,7W by setting i915.enable_psr, but that settings lead to temporary freezes of the screen.
