I agree, I don’t see where the side reins are doing any work in the first part of the video. The horse is being asked to stretch in the riding videos, which is good, but he is not really stretching with an open poll, and using his back. He is more rolling behind the vertical and just tipping forward onto the forehand. You can see the effect of less than optimal training using draw reins.
I don’t see much difference over the 8 minutes of the longe video. In particular, take your eyes off the up and down head carriage, and watch the hind legs. A big nicely built horse like this should be tracking up effortlessly at the working trot. Yet from start to finish he is still coming short behind. That says that the work on the longe is not effectively addressing his body and balance. Over 8 minutes of good longe work, the horse should be starting to track up, if nothing else, as indication he is getting his hind end working. Going short behind like this is an indication he is falling on the forehand, and the longe work is not helping him.
I’ve watched Will Faerber videos before and while I appreciate what he is trying to attempt in retraining horses that have been overschooled to overbend and go on the forehand, it doesn’t seem to me he has the most effective tool kit for doing this, compared to my own coach.
My own coach would insist on the horse moving out enough that it was tracking up, before trying to modify how the horse was moving. And in a case of a horse like this one that was rooting down, rolling behind the bit, falling on the forehand, through previous training, she would be using upward half-halts to raise the head and open the poll. Then she would move to balanced trot stretching towards the bit with an open poll, but not falling on the forehand. Only after the issues with ducking behind the bit were pretty much sorted out, would she then move to collected work and start asking the horse to give at at the poll again.Lateral work at the walk would also be started early to get the horse stepping under behind and changing its balance.
Some of this would be done in hand, as well as in the saddle. There isn’t really any room for sidereins in this scenario, if the problems in the horse were caused by side reins or draw reins.
I’ve watched my coach and her junior coach fix a number of horses with these issues, and also watched my friend fix the roll-behind problem on a new horse, with their guidance. It was never the problem with my horse, so I haven’t done the steps myself, but I understand how it works, and see that it does work. My horse had an innate tendency to invert and go above the bit, and not track up at all, so I started with working the walk lateral and forward balanced stretchy trot forever until she was trotting like a normal horse, not a sewing machine, and then we were able to start asking for poll flexion and collection.