Amen to all of that! Like most all of you I try to practice simulating real life situations, drawing and firing etc. Working in animal rescue this is a topic of real concern for me but but I have never attempted to replicate the exercise you have described. A dog attack is a very violent and dangerous event and adding a weapon to the mix only makes it a lot more dangerous. The only thing I do is go over and over in my head how I should react. I have narrowed it down to two very important items. 1. Shoot only with the muzzle literally touching the dog. 2. Be extremely aware of where the bullets exit path would be and what it will hit next. The same rules apply if I am attacked but it gets more complicated then!
There have been only two vicious attacks at our rescue in the 18 years I've been doing it. One indoors and one out. I was not present for either. One was resolved by two women foisting a large animal trap in the air and crashing it down on the dogs head. It worked, he ran off and was later shot by animal control. The other was indoors and was resolved with a mop handle beating. The dog fortunately ran into a kennel and was trapped. In either case the dog could have turn it's attention to the attackers but fortunately neither did. They often zone in on a single target and ignore everyone else. I should also add that I have issued a pepper spray canister with a belt clip to every employee but they never ever carry it.