From some of the Kabalistic work I did a number of years ago, it was also my understanding that the 'Ox' part had to do with the trainability of the animal - its domestication.
In another post (I posted a year ago today -
Hebrew Letters - Alef/Aleph), I also make mention of the meaning of this letter as teacher or leader.
One of the aspects of importance of
Alef and the domesticated Ox is that they both lead a trail. In the case of the Ox, furrows are made in which are sown the seeds to germinate. Writing with letters is somewhat similar, in that each letter, as a seed, is 'planted' in the furrow of the line. That which heads it is
Alef.
Of course, this only exegetes (or is a
Midrash on) the letter
Alef as Ox
after the fact, rather than gives grounds as to how this correlation emerged historically.
I suppose that I too have been taken in by what other scholars have in the past written, copied from the opinions of yet other scholars on the matter, and so on down the line.
It does seem, however, that the association between
Alef and the Bull or Ox does pictorially make sense, and that perhaps looking at D'Alembert may give a clue - does he not also make that correlation?
Being connected to the torso generally (& specifically the lungs according to the
Sefer Yetzirah), and being also the
silent letter which precedes sound, a metaphorical link to the Ox makes much sense (though not astrologically).
I also wonder, though had not been able to find it when I searched much earlier, whether there is yet another word in a different language group (Ancient Greek / Ionian ?) which has a word which more properly links
Alef-
Alpha with the Ox - for then, such letter association
would also make latter sense.
Interestingly, by the way, there is some evidence that
Alef is consistent with early Hieroglyphics representing an
eagle, and here the Air association of the
Sefer Yetzirah would make sense.
Of course, I've kind of rambled in this post...