Hi W2U, Welcome to the Horse Forum.
Since no one has attempted to offer any opinions, I will offer mine. You may not like what I am going to say, but everyone that has been here for any length of time knows I tell it like I see it.
It is my opinion that there are two very distinct types of training that a person needs to be able to do if they are going to be a trainer and the hard part is knowing if 'Trainer A' is needed or if it is a job for 'Trainer B'.
'Trainer A' is a patient 'teacher'. Trainer A knows when a horse is ready and able to do the next task a green horse is ready for. Trainer A knows how to 'open' that door for the horse while closing all others. He knows how to make the right thing easy and interrupts the unwanted response or makes the wrong thing difficult for the horse to do.
Punishment is seldom needed. If trainer A is good at 'reading' a horse, he knows when that horse is ready to 'push' and ask for more. He also knows when it is time to 'back off'' a little and let the horse 'work' on it and lets him 'try'.
'Trainer B' is a different guy. He has to know how to 'break' bad habits, how to teach a horse that a certain behavior is not acceptable and MUST NOT BE REPEATED.
Since I spent 3 decades training for the public, I was brought many horses with many bad habits. They ranged from simple 'tiny' (by comparison) bad habits like 'nipping' or not letting someone handle their feet or other trivial things when looking at the bigger picture. Then, there were horses that had attacked people and severely maimed them, horses that were confirmed broncs bucking serious cowboys off at will and horses that reared or threw themselves over backwards. These are really serious bad habits and the owners expected them to come home and never do their bad behavior again. A good trainer can accomplish that, but it is a job for Trainer B.
Trainer B has to figure out a way to make the horse NEVER want to repeat the bad behavior again. I have done this with many horses that reared or flipped. I never got it done by just urging the horse forward and 'riding it through' the problem. The problem just kept repeating itself over and over. If a trainer gets the horse to the point where it figures out that the trainer would not let it rear and always pushed it out of rearing, it might quit for that rider, or quit until a really difficult obstacle looms ahead. BUT, if the horse is sent home to its owner, within a week or two (sometimes the very first day), the horse will just go back to rearing with its owner or any new rider.
In order for a trainer to be 'effective' in training spoiled horses and breaking serious bad habits (we're not talking 'nipping' here), he has to figure out a method of systematic 'negative reinforcement' that makes the horse NOT want to ever do the behavior again. [I could just call it 'punishment', but I know all of people who think this is never needed will come out and crucify me.] I say 'systematic' because Trainer B needs to have a plan and never act out of anger or cross the line of abuse. This not because some horses do not deserve that severe a punishment but because it does not work. When a trainer gets too rough on a horse, the horse just goes into 'reactive' mode and from there can go into a mode of 'shutting down' or 'sulling up'. When a horse does this, it literally feels no pain and can 'tune out' any amount of pressure and punishment. This is what happens when people try to beat a horse to get it into a trailer.
I found the best way to SAFELY handle rearing and flippinf horse is to ground drive them. I have not seen the rearing horse that will not rear in driving lines. You can 'give up' all of the 'being careful' so that you won't cause the horse to rear. Of course, the horse know instantly when the rider 'backs off' because the horse threatened to rear or threatened to just stall out. When you lean forward and 'push the horse' forward and try to keep the horse from rearing is taking pressure off of the horse at the wrong time. The horse wins because the rider is fearful (with good cause) that the horse will rear over on him.
When I put the rearing horse in driving lines, I planned on making that horse learn to accept a hard pull on the reins and yield to that pressure. If he rears, I will spank his butt as hard as I can. I will spank him until he goes forward and then pull him back as far as I want.
When I get through with him, he will have figured out that rearing hurt him a lot and he HAD to give to rein pressure no matter how hard I pulled. Tolerating a hard pull on the mouth and giving to that pressure is just as important for a horse to accept as is going forward where he does not want to go. If he should rear and fall over or throw himself over, I would work his belly over until he does not want to lay on his back and get his belly spanked again. I have never had a horse retrained this way that went back to rearing. I have run into owners years down the road and their horse was still as honest as the day it left my care.
The hard part of training is to be know instantly if Trainer A or Trainer B is needed. This particular horse has learned to threaten to rear (get 'light in the front end') to get his rider to 'back off' and quit pushing him. He has refused to accept enough 'pull' on his mouth to get much done. In other words, the way he is now, he is in the driver's seat and you are the passenger.
Hope this makes sense to you.