Talking to different trainers from different disciplines, different styles and different backgrounds can be exhausting, overwhelming and frustrating if you don't have the knowledge to be able to filter the exchange of words.
I have been fortunate enough to have a strong background on a few different fields of dog training (Protection Training, Scent Work, Service Work and Pet obedience). Really you could say that all of those fields branch off the same fundamental concept that is dog training (Operant and Classical Conditioning, Establishing Operations, Behavioral Analysis)
I know, I know! sounds like a bunch of semantics and useless jargon, but this stuff is important. If you don't have a command of this fundamental principle, it's easy to get frustrated and confused when you hear different dog trainers talk.
When you hear "The only thing 2 dog trainers can agree on is that the 3rd trainer is wrong." really you're just seeing the insecurity and lack of knowledge in this field. You and I should be able to agree on fundamental principles! It's not a matter of opinion or experience, it's a matter of fact and scientific data! If you and I look at tree, we should both see a tree, not our interpretation of the tree, but simply a tree. You might think it's an oak tree and I might think it's a cedar tree, in reality, one of us is dead wrong, or both of us are dead wrong! That tree is a specific tree, not to be changed by interpretation.
I recently had the fortune of participating in an event in which three different protection clubs (mine included) got together and trained together. Overall, there didn't seem to be a major disagreement in how things were to be done. Three different training directors, additional trainers (decoys) and other members who also train dogs, none of us had any major disagreements in how things were to be done. I'm sure if all of those trainers and I sat down and started chatting about dog training, we'd find a thing here and there in which we may not be in total agreement, and that's understandable, but should disagreement arise, if we all understand the fundamental principles of dog training, we should be able to wipe off any difference of opinions quite easily. IF one or more of us didn't have a strong grasp on the fundamentals, we would then find "disagreements".