Just a short comment to the videos you posted, a bit off topic... You are right they prove nothing (dis-proving nothing either, I have no opinion on 739 vs. A321).
But, for your knowledge and to take away any assumptions (/impressions), the rotation technique used in the 737 video is plain wrong... (probably they PIC/PF was afraid of tail strike).
He lifts the nose wheel off, and makes a
long huge pause before continuing the rotation (which through-out is too slow). It provides for a magnificent tail clearance, but invalidates takeoff calculations and prolongs the ground roll. A B739 rotated correctly has a tail clearance of 11 inch (33 cm) with flaps 1 and 19 inch (49 cm) with flaps 5!!
