The OP never stated that the vet didn't have any experience with bp's or snakes. Just that he didn't specialize in bp's. So we really don't know what level of experience he may or may not have with bp's or snakes in general. But, we do know that he is a certified exotic vet.
As far as the rest of your post I agree. I stated before that the weight loss could just be caused by the stress of the continued regurges or something else such as a parasite. That is why I asked if the vet actually did any testing or just gave the 2 shots without testing.