Well one fact your overlooking (or ignoring) is that the whole FE family was created because cars were getting bigger and heavier. Ford/Mercury needed a larger motor with torque. Pure and simple, it was meant for the big land yachts of the day.

Being a torque motor meant it was good for us hotrodders, torque is what gets us off the line.

The first "series" of 396 (a real 396) was routinely beat up by a 390, the next series of 396 (402) mmmmmm.. not so much...