My understanding is that “behaviorism” understood as a field is a category of psychology that works to alter and shape behavior through the use of stimuli, whether that’s positive or negative reinforcement. It used human and animal subjects in the 1950s, but I think is mostly used in relation to animals these days. Andrew Macclean talks about rehabilitating and extending behavioralist concepts that were seen as extremely outmoded and reductive.
Thus to me a behaviorist is not just any person who tries to train or heal an animal, but someone with education and skills in a specific area and ideology. Clicker training is one small part of behaviorism techniques.
Obviously you can have a riding trainer, a coach, a vet or indeed a behaviorist who is effective and intuitive and kind, and you can also have all these people at the opposite end of the spectrum of ineffective, obtuse, and rough or cruel.
To my mind, as a psychological theory, I find behaviorism rather reductive and limited. However those are also it’s strengths. It can be very useful to have a fresh pair of eyes on a situation that will.cut through the more complex narrative you’ve created about a problem, and look just at what is manifesting in the immediate here and now.
However in my experience reductive and limited intellectual structures tend to attract people who are reductive and limited. That’s why the equine behaviorist that I’ve found useful are people who were already training and riding at a high level of competency and effectiveness before they added the behaviorist aspect to their work. They are already intuitive, capable, and kind with horses, which helps expand their approach.