As usual, there is plenty of food for thought in your post.
I have been doing quite a lot of work on backstroke and here is a sort of report I have written:
Since viewing the video of my 50m and 100m long course races at the recent Cardiff meet, I have been trying to improve my backstroke in two main areas, my arm entry and my kick. Apart from the very obvious awfulness of my start, which is just a flop into the water and as unlike the proper back dive as it is possible to be,the first very obvious fault I saw was that I was entering the hands much too wide, almost on a line with my shoulder, but not as bad as at 180º . This fault is worse with the left arm than with the right, which is odd, in a way, because my left shoulder is more flexible than my right, which I have read is normal for right-handers. However neither shoulder is so inflexible that there is any reason why my hand should not enter right behind the shoulder, especially if I incorporate a roll into the stroke. It seems to me that this must be just a bad habit and that it can be cured by replacing it with a new good habit.
To that end I have been swimming a lot of quite slow backstroke, concentrating on feeling my arm against my ear as it enters the water and raising the other shoulder and arm out of the water at the same time. I am not counting any particular number of kicks as I do this, although in the past I have experimented with multiples of three. Swimming like this I can cover 25m in between 16 and 20 hand hits, which is a lot less that I take if I am trying to swim as fast as I can, when I usually take 30 or more. My best practice time for a 25m length is somewhat over 33 seconds (I can't read the small numbers on my watch without my glasses) and so far I have not managed to come in in less than 50 seconds with this slow swimming. I take over a minute to kick a 25m length, so an improvement in kicking would doubtless be beneficial
I believe that this practice will lead to an improvement in my kicking as well as in my arm stroke, but it is too early to tell if there has been any improvement yet.
I have not so far tried very hard to incorporate the upside down underwater dolphin into my backstroke practice, but that would probably be a good idea, as would some effort to learn a proper flip turn and a decent start. The pool I swim in does not have starting blocks fitted, so I suppose I would have to practice the start with a back dive from shallow water. I can move along slowly doing a face down dolphin but on my back it is so slow as to be almost stationary.