(Which I am not!)
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>that happen to their dogs
It's a pretty normal part of dogs inter-social behaviour, as you should now the back of the neck of dogs is used by parent dogs to discipline (and sometimes carry) their pubs. In turn it's also used to make dogs submit in social fights between them. Which is a normal/natural part of there social interaction.
And yes there are aggressive and dangers dogs, too.
Still if you step in you are likely increasing the aggression the other dog has against your dog. Which if it repeatedly happens with the same dogs could make the situation problematic if you at some point are not fast enough to step in.
i understand that you describe a consistent and logical model. Unfortunately it has nothing in common with the reality i know. In one case it was a large labrador - a lot of muscle on hit back neck - so he got an inch deep wounds, a lot of stitches and drainage for a week, in another case it was Chihuahua - not much tissue - so he ended up with a series of surgeries on the bones and cartilage in his shoulders.
>normally won't kill or majorly injure the other dog but mainly make it submit
some are doing it by biting and sinking their teeth deep into the back of the neck of the victim. So it does make sense to step in before that happens, as well as to step in to stop that when that is already going on (i've met owners who had that happen to their dogs, and couple times i stepped in right before that was going to happen to my dog)