Based on how well he did in the four games, I would say there is much more reason to give him a more extended period to prove himself further than to assume he cannot do it. If you have a QB who has played QB a very limited amount in recent years, has been practicing at all sorts of positions instead of concentrating on the QB position and with all that he was able to come in and go 3-1 with a top 15 passer efficiency rating, that should be encouraging enough that you would want to continue that ride.