Devices like that are only so compact and sleek because every component was built/picked exactly for that spot. They knew what had to fit around what.
This is it. They aren't "built out of parts" but custom made on a PCB made exactly to fit into the space available.
Unless OP is capable of DIYing a mainboard PCB containing a CPU and GPU plus support circuitry and custom cooling, there is no way to get less bulky than commercial solutions. Especially not while wanting to surpass them on performance and battery life.