Some people need to carry their computer around, so the laptop has to be a compromise between stationary computing power and portability. The MacBook Pro strikes this balance quite well all around. Of course there are bigger and heavier laptops, if you require even more performance and are not limited by portability.

> isn't a desktop more suitable

No it isn't any more suitable, because you can put your laptop on a stand and plug it in to achieve the same thing.

It's not the same thing by far: Laptops have much worse heat dissipation than desktops, they overheat, and your high-powered CPU gets throttled down.