I've seen A LOT of posts about making HP with a 318-So why is it so ???

ValiantRacing said
318 .60 over Flat top pistons, 9.4-1 on the compression, cam is .545 lift 246 duration, Edelbrock heads, air gap intake 750 carb.

You don't see that combo at least making 400 hp ? I wouldn't be surprised if your more like 425-450 hp.
My 380hp crete engine dyno over 400 hp that just a stock truck long block with a cam and intake.