Time matters. Take a frozen radiator, and 200 degree water and push it through the radiator in 1sec. What is outlet temp of water. How about after 5 sec, one minute? Same with the block.
In a closed system like an engine, the time in the radiator spent cooling is also the time in the engine spent getting hotter, then microboiling starts to happen and your plan to spend more time in the radiator cooling the water off just got it's butt handed to it. Last thing you want to do is slow water flow. Max flow short of cavitation works best. Same with air flow. No one ever says " we need to slow the flow of air thru the radiator so the air has more time to cool it" wonder why?
