I've been reading this thread any trying to implement the recommendations to various degrees. There was a pretty big breakthrough through a few weeks of dedicated videos and reviewing (~18 months swimming, 1k scy at 15:16), but I'm still left with two big questions where my stroke seems to "work" but doesn't seems right.

--When going from the catch to the pull, I've really taken emphasis off of the catch and forcibly pushing back, almost like how you'd push yourself up onto the pool deck from the deep end. It kind of really feels like two separate motions, a lazy (but well placed) catch that just kind of drops the hand immediately turning into a strong push straight back. It's hard to see clearly in video where the transition takes place, but it feels like a well defined switch in the stroke. Is it worth trying to smooth this out? And if so, would you smooth it out by being more forceful on the catch or less forceful at the start of the pull?

--Arching back, specifically, with a flatter back the upper arm to spine angle is much flatter and my shoulders work noticeably harder to pull that arm to the flatter angle. It seems the real culprit for the arching back is the desire to keep the shoulder joint more extended and less flexed (at a lesser angle in relation to the spine). I'm guessing this is just something to get used to and keep working on?

This thread is truly a goldmine.