Proper form is the term used by "experts" in books videos and other "exercise scientific" books etc. It is taught in every classroom or personal training certification courses. And it is DEAD WRONG for bodybuilding. They say/teach that crap to prevent getting sued. They tell their clients to do it and that way less chance of injury and also to keep them coming back. They make little to no progress but the "expert" trainer keeps telling them it takes time so keep paying me and we will keep doing it the "right" way. I have NEVER seen any top bodybuilder or really any decent bodybuilder do "proper" form. You need the shorter range of movement to apply stress on the biggest and strongest part of the muscle to cause growth.
while nothing is carved in stone i see people using way too much weight in say the bench press & using crap form. It does not bring any muscle growth as they are simply using auxiliary muscles into play & thus recieve a poor workout for the said muscle group.
Having said that bodybuilders like serge Nubret & Sergio Oliva used it to great effect working in a small range of motion on the Bench.
The point being use a weight you can handle for the training method.
so therefor i agree with your post but again nothing is carved in stone !