You have essentially rephrased a unit of measurement to give you a smaller and less severe sounding number. Are you seriously suggesting going from 400fps to 150fps or something in that ballpark is reasonable 'when there is activity'. A few miliseconds in frame-pacing is 100% noticeable, I feel like you are suggesting that it's imperceivable or irrelevant..?
The main point of reframing it that way is to clarify how it impacts your game experience.
Going from a 2.5ms frametime to 7.8ms frametime will affect your perception of the "feel" and "smoothness" of the game, so that is definitely real, I'm not trying to say it's not.
It's an important distinction because your frametime is a component of things like peeker's advantage, so dropping from 2.5ms to 7.8ms frametime is not as significant in that context. (it adds 5ms of peekers' advantage, which is pretty minor).