Here is part 2 of the deadlift series: https://rehab2rx.ca/post/dont-round-your-back It has a deep dive on the kinematics of the lumbar spine with lifting, but also has a very simple summary. I think everyone will bee able to get something useful from this. Part 3 will cover programming deadlifts and variations.
That was a very comprehensive article you wrote. Being an "old school" physiotherapist I was taught to avoid spinal flexion with lifting for basic biomechanics. Over the years I have lost that "belief" and I've become a lot more flexible in my thinking of how people move/should move. Thanks!