It's not a heatsink by default.
The Intel MacBook Pro I had before that one got far, far hotter - almost scalding hot if you really pushed it - without any modifications.
I really do hope that Linux becomes an option in more workplaces without being too locked down for developers.
People have been modding theirs to make this contact, though. And been getting a significant performance boost out of it.
However, the fact that the aluminum gets hot during prolonged use means that it is acting as a heat sink and cooling the CPU compared to a body made of plastic. Thermodynamics, it's the law!
Not really. It's picking up "stray heat" that is radiated from the copper heatsink inside and conduction from the air in the fan system. It does not improve cooling the processor in any kind of manner. If it were plastic, the plastic would get warm too. Maybe it'll be a 2 degree difference.
Direct contact or bust.
It might be marginal, though.