That is a big and broad assertion! But one that I can entertain to an extent, lot of variables that come in to play though.
I personally think anyone has the ability to train their own horse, some horses are harder than others some riders learn faster. The key to being able to train your own horse is time you have to have time to ride. 1 or 2 times a week is not enough to train your horse. And you also have to think like a teacher. What does this horse know and what does he need to know in order to learn what I want him to know.
This part I agree with for the most part, but there is such a broad spectrum of horses AND riders that there are so many combinations that may or may not work.
Some riders are capable of training many different horses, both 'difficult' and 'easy'. Some riders may only be capable of training the 'easier' horses. Some horses should only be trained by very capable riders, others may be more forgiving of errors on the riders behalf.
The riding time comment is very true, and something that is commonly overlooked IME. The bolded part I think is the most crucial part to the above paragraph and I would like to add to it "How will I teach him and how will I ensure that my teaching is effective?" This part is something that usually comes with experience, that is, the rider needs to have GIVEN many wet saddle blankets to many horses before they begin to fully understand the importance of that statement, what it means to a horses training and how to go about it.
Next I think a person needs to develop some basic balance before they develop the ability to train their own horses. My clinics and coaching are about learning to train your own horses and I have one prerequisite for people who attend my clinics, They must be able to walk trot canter without holding the horn. With that basic balance in the saddle we can then work on discovering what type of horse they are riding and what type of basics they need to learn.
Hmmm, this might come off a little blunt, but is this the REAL reason you are proposing that any rider can be a trainer? So you can guide them through the process? You think being able to W/T/C without holding the horn is a pre-requisite, try learning English
Not much of a pre-requisite for a trainer, or a rider for that matter.
The bottom line for me is anyone can learn to train their own horse, it takes feel and rhythm on the saddle and the ability to pat your head and rub your stomach. ;O) But I have watched many riders learn about feel and rhythm once shown how to develop it.
All it takes is the desire to create wet saddle pads and to not look for short cuts.
Well, that is partly true, perhaps anyone can train their own horse with the right knowledge, experience and guidance. I think you are oversimplifying it a bit. Even the best riders in the world have mentors, learning doesn't occur in a vacuum which is unfortunately the approach that some rider/trainers take "I know best and I don't need any input because I have seen it all before."
Just as training the horse is an ongoing process, training the trainer is also an ongoing, constantly evolving process. Well, the good ones anyway