Short answer: you don't actually need to flare your knees out, but what you do need to do is generate torque in your hips which can be accomplished by attempting to rotate forward-facing feet outward ("screwing your feet into the ground") and thinking of this as pointing your knees out is a good physical cue.
Details: The reason you externally ...
Shoulder blade retraction is not the same thing as either upper back rounding/thoracic flexion or bridging/lumbar and thoracic extension.
The shoulder blades move independently of the thoracic spine, so you can have either scapular retraction or protraction occurring in any combination with thoracic flexion or extension.
The Stronglifts description of the ...
That website's contention for why a thumbless grip lessens the load on the forearm muscles is that it prevents you from squeezing the bar:
in a thumbless grip, also known as a “false” or “suicide” grip, the
thumb is held under or outside of the bar rather than around the bar.
There is no squeezing involved.
However this absolutely would not apply to any ...