There are too many things of yours to counter, Adam. So, I'll shorten it by saying you are wrong. Your lack of experience betrays you.
This is all very situational, of course. Btw, I weight 300 lbs, my dog can lift me full of the ground with me laying full weight on him and my arm locked around his neck. (Which is as big if not bigger than mine.) And no, this isn't a "my dog is superman" (cuz he is ), it's just an example of the strength of the dog. A few species of dog are capable of crushing bone when they bite. See how well any of you react when you feel your and hear your bones crunch. The problem is if you can't end it quickly enough, your chance decrease exponentially. I keep hearing, "well they only have a mouth", well that's why the fucker is so strong compared to many other animals of similar and even greater size. And don't tell me they don't use their arms. Some breeds are much more inclined to use their bodies, as well. Dogs have been used in wars throughout time. Against men w/swords and freakin armor, for shit's sake! But you're a bad ass with a buck knife. Titan held a friend of mine pinned with just his front arms and strength. Large mastiff were created with the sole purpose of being able to control a man without killing them. Have you ever had to subdue someone without physically assualting them or killing them? I have. I've been a security guard, bouncer, and bodyguard, it's not easy. But dogs can do it.
"They need a pack." Bullshit. Not all dog species run in packs. And even those normally inclined to, quite often rogue males will run lone and hunt for themselves. They may not take a bison down, but are quite capable of hunting game quite a bit larger than they are.