All rookies are going to display flaws when coming to the NFL. Whether his name is Joe Haden, Patrick Patterson, Kyle Wilson, or Kareem Jackson.
First of all, the "didn't turn his head around" is overplayed by guys who don't know what they are looking at. It's called pass interference. If you don't touch the guy, it's not interference no matter where your head is. You won't find a coach that won't teach a DB how to play a receiver face to face.
There is a time to look for the ball & there is a time to play the receiver. There is also a time when the player should play the ball but if that time has passed, he should play the reciever. Rookies find themselves in the latter situation way too often, but as long as they don't touch the receiver, it's all good. The ref may call it, but in the film room the coach is going to say, "You should have turned there, but you didn't. You recovered fine, don't worry about the ref."
Then as far as turning his hips..... you either got it or you don't. You're not going to take a guy who doesn't have it & teach it to him in three years. Learning how fast an NFL receiver will get on top of you, learning how fast an NFL receiver will blow right past you, learning how strong an NFL receiver is, learning how fast and strong an NFL receivers hands are, even the most NFL ready corner is going to have a learning curve here, regardless what his name is.
Do you not think Joe Haden, Kyle Wilson, and Patrick Peterson are better at those basic cornerback techniques now than they were when they were rookies? Do you think Glover Quin & Devin McCourty might not have that ability & maybe that's why they're playing safety now & not corner?
If I've got Derrell Revis on one side of the field, then I've got help on my side of the field, I'm not on an Island as much as Kareem was. I'm able to face the QB longer & jump routes, and gamble. My mistakes won't look so bad, because someone is going to stop Roy Williams from running 70 yards to the endzone.
If you watched Kareem play as a rookie, you could see he had speed, he had cover skills, he was physical at the line, & he was a sure tackler. He made some rookie mistakes, he got beat by some veteran receivers (& some not so veteran receivers). But if you only focused on the bad plays & did not pay attention to the good plays (& there were a lot more good plays), then yeah I can understand thinking he was the worst CB in the league.
But to believe he went from the worst CB in the league to one of the best in 3 seasons... yeah, that was all coaching. I understand if you don't think he's one of the best, but he is.