The intake valve is larger requiring more lift to see maximum flow. The exhaust is opening with what, 100 psi pressure? Plus it has the big advantage of exhaust scavenging. So intake and exhaust are two totally different animals. When a blower is added to the mix, now you have much more force to fill the cylinders. And a lot more exhaust volume to expell. That is why forced induction engines will perform better with a somewhat larger exhaust valve and a bit smaller intake.