Obviously there are light-years of difference between AA & Major League pitching. That said, I don't think there are many pitches in the majors that Buxton hasn't already seen. Just not with anywhere near the frequency or consistency. I'm not certain that batting ninth and struggling in the majors would be that detrimental to Byron's development, as opposed to leading off and fairing somewhat better in AA. In addition to having unfettered access to daily mentorship from the likes of Molitor, Brunansky, Hunter & Mauer, he would also have use of what I can only assume are superior video and training facilities at the big league level. Whether in Mineapolis or Chattanooga or Rochester, he's still gonna need to learn which pitches he can handle and which ones to let go.
In spite of all that I think the Twins best option if Schaeffer isn't cutting it, is to go with Hicks to buy time. We know the defense would be adequate and if he tanks again quite frankly, who cares? Three strikes and 'yer out! This is baseball afterall.