Either way you are working for a machine to dominate now or eventually an activity that was once human.
Centaur or reverse centaur is no longer human being. One is either a working horse or a pasture horse in these scenario. Human is destroyed either way.
Maybe that's good. But who would be lucky enough to be half Chiron, and who would be those stuck with being half of the rest of the centaurs ? The argument denigrates humanity if those are the only to choices.