I am thinking people can and do use the terms mild and aggressive as a quantifier of efficiency. The head design of some razors because of the blade gap, blade exposure and blade angle make them more difficult to use to get a comfortable shave with.

I mean my Muhle R41 2013 version will give me a longer lasting shaves than my Merkur 37c slant. The Merkur slant is much easier to use as it is more forgiving of the angle it is used at and pressure applied compared to the Muhle R41. Both will give comfortable shaves for me. To me the Muhle is more efficient/aggressive as it gives a longer lasting shave.

So basically some DEs by their head design become so aggressively efficient at removing stubble they are more difficult to get a comfortable shave from. To a large extent efficiency and aggressiveness can be the same thing. I mean even what is considered a mild head like the Gillette Tech can give uncomfortable shaves for a beginner at the start.

Where aggressive and efficient diverge is in the skill level of the user. You can't change the head specs of a DE, with the exception of the adjustables, so the efficiency remains the same. The user may not be able to properly use the efficiency of a DE head design so it is too aggressive for their skill level leading to uncomfortable shaves.

Bob