I agree there is only so much out of a 318 head vs say a j head. main reason is its two different castings and the runners are cast bigger in the 360 head. You simply cannot hog a 318 head out big enough to match a J head.
And the port on a 340-360 head is too small for even 318 inches. Even at 5500.
So you jam more cam in it to make it rpm and the torque takes a massive hit.
More torque and driveability is killed by a big cam than a head thats “too big”. I see it all the time.
Where did my torque go? Well, you **** the torque because your heads are too small, the cam is too big and you don’t have enough compression to get it back.