>If what you suggest was truly necessary, wouldn't most complex dialogue in fiction be incomprehensible?

...no?

Fiction (or really any prose) has context and continuity, so it doesn't need to disambiguate. Context and continuity are lost when an excerpt is lifted as a quote. Hence the usage of [brackets].

Since this is painfully obvious, I'm struggling to see what did you mean to illustrate by referring to "complex dialogue"?