I am not surprised that our "good posture" is cultural rather than science based.

I will definitely look into PRI exercises, but I am a little discouraged even before starting. I have congenital hemihypertrophy (greater than normal lateral asymmetry). Everything on my right side is much bigger and stronger than on my left. Leg and arm lengths, shoe and ring size, size of the bones and muscles, eye size/prescription, etc.

On one hand, I wonder whether I could do PRI exercises "well enough" for it to help me. On the other hand, knowing how asymmetrical my body is, maybe PRI is "made for me". I hope it is the latter!