If you lack lumbal extension (lordosis). Front side mechanics will be to excessive. ALL elitesprinters lumbal extend. But i dont have any peer review studies, so yes its just a statement.
Anyways i know you cant provide a video close to your PR where you run without lumbal lordosis.
Also their is a ton of theoretical explanations and evidens that lack of lumbal lordosis leads to protrusions in posterior direction,
Their is a difference between hyperlordosis and normal lordosis. Your saying no lordosis = flatback which is a pathological structural og functional deficit.
The next comment is in relation to thoracis extension. Your commenting on lordosis.
The analogi is:
Decreased thoracis extension = Compensation with lumbal hyperlordosis (people overextend the back) = increased injury risk and performance
Why Front squat are good:
Hamstrings fixes pelvis at bottom position so forceful extension of the thoracis spine is possible without anterior pelvic tilt (which is results in lumbal hyperextension).