When boundaries leak, it's important to distinguish commitment to rectify them from credence that they didn't.

These are all failures to acknowledge the natural boundaries that exist between individuals.

I think a lot of what you wrote boils down to "it’s hard to both set and respect boundaries if you’re too insecure", which should probably be / is kinda supposed to be "Not Being a Jerk 101" or something we learn as children, but I guess a reminder is always welcome—I certainly could have used it sometimes myself. 

The way I see it is that "boundaries" are about the fact that you can’t decide how others feel, or make them feel in a certain way. If someone comes up to you saying that blue is their favourite colour, you know it wouldn’t make any sense to force them/coax them/gently sweet-talk them into believing that red is better. You can, say, convince them to paint the shutters in your house red anyway by using rational arguments, that the bylaws of the neighbourhood say it can’t be blue, or that the store’s run out of blue paint, etc., or emotionally persuade them by saying that you really like red and you’re both going to live in this house and are they willing to make a compromise? But you can’t say "look, dear, I really want you to like red better/I’m sure deep down you really like red better". 
And, in this toy example, it’s pretty clear.

But in social contexts, sometimes that’s different, because, as you said, it can be rational for children to be afraid of their parents disliking them, and, more generally, a lot of our social interactions are run on that sort of emotions: "I don’t want X to dislike me, I’m afraid X dislikes me". Which is kinda in contradiction with what we just said, that you can’t control people into feeling a certain way. There’s something to learn by practice that is more or less "Ok, I really don’t want that person not to dislike me, but they do anyway, and I can’t prevent them".

We could then, as you do, phrase it in terms of control: having good boundaries is knowing that you can’t control others, or, as I put it, knowing that we can’t force them to feel a certain way. There are a lot of people—sometimes including myself—who, mainly due to insecurity but also to other things, really want to feel like they’re in control, which makes it relatively hard to notice that while you can control how hard you work, you can be really ambitious, etc., there’s still that huge thing out there you can’t actually control and shouldn’t try to control, labeled "what other people think of you". That’s something you can only influence by, say, not being a jerk, and by treating others well. Which includes, incidentally, "respecting their boundaries".