We must be twins!
I could have written those same sentiments and likewise practice similarly.
I totally agree with and have experienced similar nuances while practicing especially your comment on the breath and stroke timings.
I've been hard pressed to get any consistency in practice time (work/family) but have maintained rrcent 'efficiencies'.
In my last go, my main set consisted of a re-visit of rounds of 3x100s (scy) with the TT.
I kept tempo range pretty close as I focused to draw out all those nuances you mentioned in hope of improving "effortlessly" (remembering that to become truly "effortless" takes great effort).
My tempo range was between 1.07 and 1.01 for this exercise and kept me well within my spl range too; this pleased me most. My task going forward, to become comfortable at higher tempo rates and spls and hold same efficiency; duh.
I swam 50BK as active rest between each repeat and round. My times improved from 1:25 @ 1.07 tempo to 1:21@ 1.01 tempo, so happy with improved times while staying within my stroke efficiency range.
Eager to 'hear' more...
P.S. happy to go over any specifics...always