100% this all day. This is what this entire thread distills down to. It feels like such an F-U by Apple to blatantly disregard the fact that other Macs -- older and weaker Macs -- can drive 4K displays with an integrated GPU.
I don't like knowing that I've paid top dollar for a high-end machine, but that machine, for as nice as it is in other dimensions, is inherently flawed in a major way. As
@leonchu1225 said, for many of us chained to our desks at home, we're always plugged into our monitor, always hearing the fans and living with the fact that our MBPs are being cooked to death, reducing their lifespans, for no reason other than either (1) an unfixable hardware design flaw that forces dGPU to always be on when plugged in to an external; or (2) Apple and/or AMD's unwillingness to revisit their dGPU drivers.
I know Apple is capable of producing the best laptops on the planet, but these 16" MBPs weren't it, despite all the marketing around the new thermal system.