I think Maton should go to winter ball to play OF, right now he just doesn't have enough experience, which is why Guthrie's been playing OF in Lehigh, adds value if you add that to your repertoire - but you need enough experience to gauge the flight of the ball off the bat - otherwise he may be worse than Schwarber even with better tools.
Hall lacks the athleticism to be even below average in LF, same reason they probably haven't tried Sands in the OF in AAA, they DH him when Marchan catches.
Vierling playing IF, Maton playing OF, Guthrie playing both makes all three more valuable going forward in an age of short benches - which is why trying to do that with Kingery was the right idea - he just forgot how to hit the ball.