There are far more energy-efficient ways of generating that heat than PoW. This is an (extremely) flawed argument.
PoW is roughly akin to resistive heating. Heat pumps are about three times as energy-efficient as resistive heating. This does not even begin to take into account that there is no practical way to transfer the heat generated in massive server farm installations to where it would actually be useful without incurring massive losses.
In terms of a kettle or cooking you're right, but you also can't cook/boil using mining hardware as they're heat limited to ~100C. For hot water heat pumps work great.
> Also, heat pumps don't really work in colder climates as the only heat source.
Ground source heat pumps work just fine in cold climates and have been rapidly getting cheaper.
... Oh.
Which then results in situations like miners buying up the majority of new GPU releases, leading to shortages for any other users, and still not having enough to keep up with the difficulty increases.
You didn't take into account, that:
Therefore, it seems that the heat demand of humans can run the Bitcoin network securely, even without block rewards. It won't "eat the world", but find a beautiful balance.