kernel_task using 100% is the system thermally throttling and the OS spamming NOPs to cool the CPU down
I don't know much about CPU internals, but this sounds like bullshit to me. A NOP is still an instruction that uses a cycle - why should that cool the CPU down? The CPU frequency should get reduced to lower the power consumption and hence the temperature.
Any way to see that?
This is usually not the case.