It is not always a heat problem, i had this when my battery was dead. There are several hardware faults that can trigger the kernel tast throttling. If the cpu gets too hot the cpu itself throttles. If there is a problem with the fan or heatsink and it's still too hot, then os x reduces the load on the cpu thats throttled to the minimum clock to an absolute minimum. Kernal task throttling is also activated when one of the sensors apple places everywhere in the macbooks reports a high temperature or is faulty. A faulty sensor is not an uncommon defect.
With all respect but each point you highlighted is connected to heat - so it is clearly a heat problem we have.