From the way you describe the drill in the initial post, sounds very similar to the "four step" presentation drill that GunSite (and probably others) teaches.
The idea (as I understand it) is to keep the off-hand from being swept during the initial presentation, yet getting the off-hand into a two-handed grip as soon as it is practical to do so.
IIRC, they advocate that one should practice this form of presentation daily (15 minutes, 100 repetitions, whatever) until it is rote.
I can see that if you are in a "non-standard" (whatever that is) encounter such as grappling with a BG, this ritual may place you at a disadvantage.
I can see that this can present what seems to be a quandary...and I do not speak for any trainer or organization. My understanding is that we train most for the most-likely situation.
Add another variable--the same situation exists for those who carry OWB sometimes, and pocket-carry other times. When "It" happens, will your hand go to the wrong place? Can you ingrain several different presentations into your sub-conscious, and select the right one when the adrenaline is flowing? (Doubtful, IMHO).
Or, can you commit to that 15-minutes-or-100-presentations every single day, without fail? And even if you do, you are either training for the "four step" presentation, or for a "retention" drill. I know someone who dedicates the last 15 minutes of a range session to strictly "retention" drills...if the range he is visiting allows it.
Lots of questions, none of them easy. I suspect most of us are somewhere in the middle.
FWIW, I have historically tried to limit my "change-overs" to "Winter" and "Not-Winter"...and in the last couple years, I am trying to just settle on one handgun and one carry method, and stick with it. year-round. That eliminates one of the two variables. Not sure how to eliminate the other.
I am not a low-drag, high speed dude. I am heading into old-fartdom. My range does not permit presentation from a holster, double taps, or other "advanced" techniques...and that is fine. They are running a range, not a school.
Sorry for the novel. It is a question worthy of thought and discussion, and we all may learn something.