No, a small finned heat sink with no air movement would be worse. They are spreading out the heat to move it out via a large surface area of the metal case. I'm guessing the paste wouldn't help much since the heat flow density is fairly low. Think of it this way, the thermal resistance per sq mm is relatively high, but the total parallel thermal resistance is still very low because of the large area.
Don't forget, this machine is focused on the consumer mass market, not the high performance market. It will never break a sweat for the vast majority of typical use cases. Even when throttling a little bit, it still vastly outperforms the Intel MB Air it replaces.
Get a 14" MB Pro if you really want incredible thermal performance.