These things will either come with experience, or they won't because he gets an infield job next year.
I highly doubt he'll be at CF next season. The CF's job is to cut balls off in the alley and rob hitters of xbh and the occasional dinger. Most times, the angles are easy except when its hit right at you, but when it's behind you then it's an adventure. Dusty should have kept trea at CF even though I don't like him there, because if he's the starting CF in the playoffs he better get as many reps as he can.
I was really upset when he didn't play CF at ATT. I don't know if it's because Dusty didn't trust him there as it's one of the hardest parks to play CF at, but he should have been the starter to be challenged and learn the position. CF do not get that many hard chances, but when they do it's really difficult. Plus just in case the nats were to play the giants (it doesn't look like they will) he would have some experience playing in that yard. Even now, Dusty is moving him back and forth. It's not a position that he excels at yet. He has to tools, but not the experience so it makes no sense of dusty to not give him that experience. Even dusty has mentioned that he worried about trea learning new things like crow hops and banana routes and having to learn how to throw differently. Infielders typically throw 3/4 or sling it low like Rendon does. You can't throw like that when you're an outfielder because the ball will tail away from your target and you can't get as much mustard as you can throwing over the top. I've played CF/RF for 36 years and have seen infielders screw up a lot of times when they had to fill in because we were an OF short that day and some of these guys were ex college/minor league guys who have shagged balls and thought it would be easy.