The amount of raw power you can drive will "always" be contingent upon your ability to dissipate heat. And the second law of thermodynamics being what it is, that ability is relative to the space you have (assuming you're using similar cooling technologies in both cases).

Laptops being power-conscious, they're usually much closer to the point of maximum efficiency on the power curve. In that sense you get better performance per watt. But that's negated by the increased front cost.