Just wondering if it could be a "tight" bit of the glass slider guides? In my experience there's always a bit of slack in these sort of mechanisms and if the window glass is binding slightly in the guides in the middle of it's travel, then it will hang up a bit which allows the mechanism to use up this slack before overcoming the tightness and the window then drops a bit as it continues descending under gravity. Try starting with the window fully up and get an assistant to slowly wind the window down as you grip the glass on the inside and outside with both hands and exert a downward force on the glass. If it goes down past the point at which it seems to hang up smoothly without the hangup then I'd guess the winder mechanism is Ok. - In fact you may actually feel the "tight" bit - If there's tooth damage you'll probably feel this as it transitions the damaged tooth/teeth.
These mechanisms are not usually made from hardened steel and, if the damage is to the pinion teeth only, can be very successfully repaired by welding metal to the worn teeth and filing back to profile. The pinion wheel is a bit more difficult though.
Referring to your video, if it was a problem with the teeth, would you not see it manifesting itself on the way up too - maybe even worse on the way up?
