That's misconception. High speed stages are where engine counts the least. Engine playes the highest role in slow twisty events instead.
It's not like the main difference in the engines would be in peak power. The real difference is in power band (or torque curve if you like). It means that where you really get to see the difference is when you have plenty of slow/medium corners where the engine needs to accelerate over wide RPM ranges. In very fast stages it is much easier to keep the engine in the peak power RPM range (naturally it's the easiest on a straight and it's getting harder and harder with how twistier the stage gets).