Hiya Ken, I see advice as the sharing of experience rather than instruction, so for me all of it has value.
Dodgy shoulders or not that swim sounds hairy! Hat off to you. I haven't yet been comfortable swimming in the lake when the wind gets much above 2m/s
I find Coach Dave's dryland catch drill injures/or aggravates a weakness in my shoulder. So I experimented with it lying on my back. I found that when my elbow bends my upper arm automatically comes level with my shoulders. Trying to reduce this action then opens up an exploration. You can find what is required in terms of flexibility etc for catching earlier and, there's no gravity to deal with on your back so you can easily explore all the muscle strengths/movements involved.
FWIW, and with all your caveats (of course), I find the form of the catch is related to timing and roll, and those to the tramlines and etc etc. When the overall form of my stroke is right I've found the form of my catch is created automatically. Shame that only happens once in every 50 strokes!! :D
A psychological disorder is: "Any personal construction which is used repeatedly in spite of consistent invalidation."
~ George Kelly
"The water is your friend.....you don't have to fight with water, just share the same spirit as the water, and it will help you move."
~ Aleksandr Popov