No it is not, as Pit Bulls were bred to be family dogs - loyal to people. Strong and able to protect the family, but also loyal to where they do not turn on their owners, and for the ones that were bred to fight other dogs, also had to be pulled from another dog by the owner without the fear of the dog biting the owner.
Life experience does not quantify normalcy. Sorry I have to tell you that. We call those "Anecdotes." Anecdotes have no place on the debate table, which is unfortunate for you, because it seems to be what your entire stance depends on.
You want the yorkie to be something it is not and that is what I don't understand. I love yorkies exactly how they are and I have to admit it makes me smile when I read people describe their temperament, watch videos like above, and see other videos of other people's dogs that remind me of mine.
You on the other hand can't seem to come to terms with the facts about Yorkies and that doesn't even make sense.
You have a calm and mellow yorkie - which is awesome. However, I don't think you can provide much help in helping others train yorkies who have more stereotypical yorkies. Feisty, aggressive, highly energetic, etc. seems to be what most people deal with.
More people talking about yorkie behavior in this video here:
Meet the Breed - Yorkshire Terrier - YouTube
Notice the trend? Everybody seems to say the same thing as me. Funny, none of these videos or publications describe the behavior you describe.