I will give it one more shot & then let it go. The answer as to why MLB does what it does with their pitchers is that when you get to MLB they are not going to "command" you to alter your routine. If you decide, as I did as a reliever, that the simplest thing to do was go 100% stretch, then you are not going to get much pushback, if any. It's about results. If the stretch simplifies mechanics & helps a guy get people out without a loss in velocity (largely because everyone has a horses*#t full windup), then 100% that will be the trend.
One last example to illustrate why " nothing matters before the leg lift" is incorrect. If I was pi##ed off & was going to slam a door, how would I do it most effectively? Would I pull it back, stop (arrest all forward momentum & elastic energy at top of leg lift) & then crank it shut? Or would this instead be one fluid motion of cranking that door back, stretching the core, arm, leg & back muscles, creating energy & slamming the door in one dynamic, fluid motion? Yes, this would shatter the hinges.
Just PLEASE go pull a Nolan video from the full windup & come back & tell me there is no energy generated, that translates to the delivery, before leg lift. This is all I ask & I am done.