You can debate this forever, we will learn a lot more soon, when preseason gets started. Neither player has really had a clean season with a normal training camp and preseason. This could be the year for either or both to really show what they got.
I keep thinking of Avery Bradley. He was really bad his first season (also very young) but you could see flashes of the ability. He didn't average double figures in points until his 4th season (at a young 23 years) and from there, he settled in as a very decent guard in the NBA.
That is what I see for both Nesmith and Langford. They will both be 22 in October, about a year younger than when Bradley kind of settled in. Langford has durability issues that he needs to get through and that is always a kind of wild card but I feel either or both of Nesmith and Langford could develop into an Avery Bradley level player, which is not a bad outcome. Much like Bradley, what I see are two players that have the ability in them but so far have not developed the required confidence and other mental/emotional aspects of the game.