I'm sorry but as a former player and GA for various D2 and jucos after college, i can tell you your bolded statement above is 100% false. Mechanics is more than just arm angle- its dropback/step back cadence and timing depending on the play, its consistent footwork that is always in motion and ready to throw at a moments notice and not being off balanced, its about maintaining proper balance in and out of the pocket so you're not leaning back (as the TM video above tried to point out), its about engaging the core and hips in the right way so you're using your whole body to throw with power (not just with pure arm strength), accuracy and consistency. All of which is before we even get to arm angles/releases and timing w/ receivers. I haven't even touched on head movement/eye movement to not telegraph where you're throwing and deceive a DB into covering a guy you aren't throwing to. All of this (and much more) falls in QB mechanics