I can't agree with this. What you are saying is "the first step is slow, so there is a "slow" between the middle of the last quick and the middle of the first slow" (have i understood you correctly?).
The middle of the last quick is exactly that - in the middle of the last quick and therfore not part of the first slow.
My original point on all this is that most dancers - even advanced dancers - plant their foot on the note because the note defines the beat (i was talking about simple 3 notes-per-bar waltz, and still am just for the moment) yet the technique books effectively place the step boundaries on the & beat (between the notes) which can be danced no problem, but is a source of confusion for those learning.
Transferring my comments to foxtrot (and taking a big risk!!)i would maintain that i plant my right foot (first step of feather) on the beat and so the preparatory act of moving the right leg past the standing left leg, sliding it across the floor (with my body following appropriately, in case anyone points it out!)takes place during the previous & (usually 4& in my case). Of course, i do attempt subtle rhythmic variations to interpret the music - with limited success - but this is the essential timing i use as a base. I'm prepared to do this differently if i can be convinced that good dancers do it differently, but from videos i've watched, i'm yet to be so convinced