You guys are seeing very high temps (80c) at quite low clocks (2.2 ghz). I just ran a quick test on my XPS 15 9570 (also one of the thinnest & lightest and thus most thermally-constrained laptops with the i7-8750H), running a 12-thread stress test at 2.2 GHz. After 1 minute, temperatures on all cores held at 52C and the fans did not come on. Again, the MBP 15's behavior is telling me that the cooling solution is just woefully underdesigned, and there is nothing that can be done to get these chips to hit their potential. And these are brand new macs, with no dust in the fans, no dry thermal grease, etc.
Now i googled the XPS 15 9570 and it's quite funny, how people are talking about thermal problems and undervolting it and how Dell did not change anything to deal with the increased heat.
And the temperature you seem to be getting, is the idle temperature for other guys with this device. So you must have quite a special one.
Some quotes:
So after pushing the computer a bit at stock:
I get an ambient sensor telling me 121 C and cpu maxing out at 93 C. This results in CPU throttling all the way down to 800 mhz.
It is my belief that on heavy long workload, the i9 will throttle to the same level of the i7 (even if you undervolt etc etc). Save the money and get an i7.
Oh and they realized that they are not alone:
Looks like the Macbook i9's also throttle
Sound familiar?
http://forum.notebookreview.com/threads/xps-15-9570-owners-thread.817008/page-71
And also a youtube video, talking about it
You can find plenty more on google.