I think we agree on the fundamentals - as flight animals, horses are bound to experience stress over new things. And we agree that stress is counter productive to learning so something needs to be done to manage the stress and reduce it. I’m saying that R+ is a very effective and easy way to reduce a horse’s stress levels when new things are being asked of it, because they learn that learning can be fun for them, and it’s enjoyable rather than scary.
All I can say is that this doesn’t bear out in my experience with R+ — with dogs or horses. Even my very food motivated rescue dog, when I first got him, was so anxious that he wouldn’t eat treats offered to him, let alone perform a behavior to get the treat. He still often won’t accept treats from strangers. And I’ve had the same experience with my horse. He’s happy to perform all his clicker trained behaviors on nice, sunny days in a familiar place. And yes, for specific things that used to trigger anxious behaviors, like pawing at the mounting block or throwing up his head for bridling, clicker training was able to strip the anxiety out of those experiences so that he is eager to show off those skills. But that’s because, in addition to using the clicker to countercondition a response, I was also able to consistently reproduce the trigger until he was pretty well desensitized to it and even had a positive association. Unfortunately not every circumstance you find yourself in with a horse is as easy to reproduce as bridling or standing at the mounting block.You need more tools in the toolbox to safely manage and redirect anxiety than just waving treats and consistent exposure to the environments that seem to put your horse over threshold.