They live in a perfect world. VVT gives them the correct timing at all RPM's, and conditions. Fuel supplied the same way. Cams and heads and intakes that all live in a matched world. Then, they are backed by 6-10 speed transmissions in bodies designed for air flow/dynamics
True, not saying you can do it a 100% exactly with older engines, but mainly with the right heads or head mods you should be able to get decent hp 350-450 hp without going too crazy with cam and compression.