I think by its very definition learning theory is not generally classified as a hard science. At least when I learned it academically, it was in my psychology courses....an entire course devoted to brain and behavior, entire course devoted to learning, under the bachelor's degree of psychology, which tends to be classified as soft science.
Bailif, to me what you said "there are trainers with huge gaps in their knowledge who can accomplish a lot" means it IS a little subjective.
Who is to say who or what is absolutely right and absolutely wrong when it comes to dog training? It isnt like math where there is only one right answer.