One thing that does get lost in translation about anything mid 70s onwards was that testing and ratings changed too...
Early 70s engines could and we're tested on a stand, with NO accessories (not even water pump), open headers, non-factory carb and timing, etc. And that was considered normal/acceptable.
Go a few years forward you've got snog motors, unleaded gas, had to be tested with FULL accessories in place and running, and, factory type carb settings, timing, etc.
So, it's easy to knock 70s-on motors, and rightfully so. BUT, if you tested the earlier motors to the same standard you got in the late 70s, SOME, (not all) of the difference would disappear as well. That was the whole "gross vs net" issues - nothing to do with post drivetrain losses like it sounds, still flywheel. Screwed with the testing again in the mid 2000s too.