"The device is plugged into the provided external power supply, so it is not running hot." Being plugged into external power has nothing to do with whether it's running hot. It just means it isn't depending on your TV for power - the heat produced is exactly the same.
Is this a first gen firestick? I have noticed that my first gen firesticks have slowed down significantly since the 18.104.22.168 firware update. The 2nd gen firesticks are fine so far. I think the first gen firestick CPU power is inadequate for the latest update and most likely will continue to be so unless Amazon do something about this.