I won't argue with your thought. I'm certainly no accredited expert either, just a dad that, along with my wife, raise 4 daughters and pets - mostly working hunting dogs.

My take is that baby talk is impossible to do in a loud and angry voice. And is always done in a soft and gentle tone. I have noticed that when training dogs, I'm a fan of Spaniels, that if you are speaking in a loud voice and that has angry tones, they will start to separate from you and watch you closely. Because ain't no one wants to get yelled at. It's kind of similar to loud sharp barking I suppose. Cats though, are generally arse holes and just don't care......

When our Daughters were newborns, they started to make just sounds after about a month. So baby talk was was pretty much just making intelligible sounds back at them in a soft and soothing tone. As they started to actually learn and use "real" words, less baby talk and far more normal speech is used by parents I think. But children are also smart enough to know the different between the baby talk when playing peek-a-boo with daddy and then need for normal speech at other times.

I certainly don't see baby talk to infants and small children as an issue except in rare disfunctional family situations.