He's a guard.
You can put him at "PG", but only if there is a second passer at either SG or SF.
You can put him at "SG" but only with a PG who's able to function without the ball, because you need it to be in Reke's and Cousin's hands. This is a well known formula to anyone who's ever watched Wade/Roy/Kobe etc. function.
Now, because of the existence of Thornton, there is a problem. Thornton is a pure SG, too small to play SF, way too selfish etc. to play PG. So unless you send him to the bench, the only available guard spot for Reek is PG. And Thonrton is certainly not that second passer in the Reke as PG scenario. So then you are stuck looking for a SF who can pass and help. Whihc is actually what we tried to do with Salmons despite how dumb that looks now, and with AK47, who is very underrated passer as a SF. Other options are tough to find/acquire. Igoudala could do it, but he can't shoot either and so is a poor fit that way. LeBron is, last time I checked, unavailable and moderately ball dominant. This is our difficulty. But difficulty or not it does not make it the players' fault when HE is the guy moved out of positon to try to accomodate the roster. If Thornton was moved to SF and struggled, it would not be his fault either. Nor if Boogie is moved to the point.