The 4th pick in the draft can only be an impact player if there are impact players to take. This was a very weak draft at the top.
Take a look at the NBA's rookie ladder...
http://www.nba.com/rookie-ladder/I can't say that I'd want guys like Klay Thompson or Kenneth Faried over TT at this point. Sure, Klay is shooting lights out, but I think we can get a more dynamic wing player. Kawhi Leonard would be nice to have and the jury is still out on Jonas V. I don't think you can really start hating on this pick until at least the end of next season.
I get that we want to see more from our 4th pick, but we have to give him time to develop. He's playing on a pretty depleted team with no training camp or off season conditioning program. There have already been glimpses of really solid production. He's gonna be a garbage man kind of player while his offensive skills develop, but those players become undervalued when the rest of the team is garbage as well. I think next year when we have a couple new scorers on the team, Thompson will look better and have a more clearly defined role. At least we know he can rebound and block shots and hustle.
Also, look what Timmay says about TT:
Before the Cavs' 35-point loss to the Spurs on Tuesday, one future Hall of Famer had high praise for the rookie. "He's impressive," said Tim Duncan, who worked out with the Texas product in the offseason. "Obviously, his length is impressive and the ability to already use both hands around the basket is impressive. He's already light years ahead of me in that aspect. I think he's got a very bright future in this league." I think "light years ahead" is Timmy being uber-humble, but Thompson is definitely proving he has a bright future.