Bull crap.
The pecking order is adjusted every time a member is added or subtracted.
It also changes as alpha gets older and the younger gets stronger.
We had dogs at home when we had our first child and none of your fantasy played out.
Well, I wouldn’t put it that way, myself, but a big part of the problem (or “the” problem) is when dogs are allowed to maintain “alpha” status in the pack. The owner is the alpha. Or they better be.
I would never leave an infant or small child alone with a dog, period- no matter the history, how much I might trust them, or how much they love the kids.
I don’t leave my dogs home alone to fend for themselves if there were a fire or a break-in, either- so maybe I’m just weird.
This ^.
Pack hierarchy constantly changes, often imperceptibly, sometimes moment by moment but usually so subtly we humans never notice.
The pack is fluid.