Here’s Ubuntu Kylin 18.04 LTS. ships with UKUI Desktop as default desktop environment and Powered by Linux Kernel 4.15 series – Info Linux

the problem is the CPU and GPU the shell uses

It’s pretty difficult to find the issue without any logs and such but as your setup was a gaming laptop with (I guess) 2 GPUs (onboard and external) it might have been because your external GPU was active instead of the onboard one? I can only guess here because my laptop never uses the fan on GNOME3 except running external applications that need some CPU power. And yes, the GNOME shell isn’t the best and it has some issues that hopefully get fixed with time but it’s not so severe, honestly (except that one memory leak bug I’ve linked).