You keep citing this Fitch work on animal bellowing as if it is somehow conclusive. Again, as the Lieberman 2007 paper makes clear, it is the position of the tongue that is crucial. You have not addressed that fact at all.
MacNeilage's work on infant babbling again highlights the importance of things other than just the larynx descent. Does Chomsky have a position on babbling?
Another problem for Fitch, as the Lieberman paper points out, is the evidence that humans are expert at discounting differences in vocal tract length in order to hear a vowel as the same, no matter whether it is said by a lisping toddler, reedy adolescent or husky adult male.
So for animals, we have a descended larynx for sexual display where size counts. But for humans, we have the reverse story of size factors being actively filtered out so as to focus on the message.
So much for a case of convergent evolution.