I still don't buy it, and the math is off due to missing variables.
Wattage doesn't create heat, resistance does.
Hotplates and processors are both built differently for different purposes. Processors are using the majority of their watt energy for processing, therefore the resistance heat isn't as efficient per watt. They are also built of material which doesn't hang on to the heat for a long period of time.
Where as a hot plate is using watt energy and creating as much resistance with it as possible. Therefore it is more efficient in creating heat with each watt. It is also made of material which is designed to hang on to heat as long as possible.
A brick holds heat better than a sponge or a block of silicone.
Now, reconfigure your tests using the above information, and you'll forget about wattage vs size.