Apple seems to have a long (and poor) track record with dGPUs, though admittedly a lot of the problems seemed to have been resolved beyond the 2011/2012 models
the mid 2015 dGPU fired up the fans just by connecting an external display and playing a youtube video. it was absolutely awful. while it didn't make any noise on it's own, it was disturbing trying to work in the fan noise. the 2016 with the radeon pro dgpu was at least quiet under normal load and in PS, but it blacked out when disconnecting it in clamshell mode while connected to an external display. the touch bar would lock up, the only thing lit was the keyboard and the sound still rolled, but everything else was black and didn't respond. it is a reproducible error and is present in both the 13" and the 15", and even happens with the new LGs that were made for the new macs.
I have owned 4 models of this computer. One 13", and three 15". One of the 15" had a bent chassis, you could wobble it on a flat surface. Another displayed white tint across the screen and adjusted volume and brightness on it's own. All three had issues with external displays. Getting peripherals that supported USB-C was hard, even though the standard has been on macs for over two years now. Many people are trying to make hubs, but few of them arrive to market. Kickstarters and the like all fail to meet demands.
I spent three months just trying to get things to work. I ordered cables and docks, but they all seemed to have quirks. I had to make compromises from the beginning. Finally my wife told me to just get rid of the computer and get a refund. I felt like I paid 3000 dollars and upwards just to betatest this device.
The Touch Bar was fun for a week or two, but it never grew on me. It's great for the last two pro apps in Apples portofolio, Final Cut Pro and Logic, but even with support in alot of the programs I use, they never really made sense, since I had to stop my workflow to apply "touches".
Now typing on my stable MacBook 12 from 2015 instead of any of the new Pros. Now I am wondering if I should buy the mid 2015 with Iris Pro just to have a computer at hand with four cores and native support for macOS. The Mac Pro is labeled a misstep both from "Pros" and Apple itself, so buying it would be a total loss as fast as the modular Mac arrives.