No one said it was "the" problem. You're trying to single it down to one thing and it's simply more than just one thing. It's the rules, the disparity of size between WR's and corners and the type offenses being run etc. To address the never turning around and looking for the ball "in phase". The DB's are taught to take keys from the WR in order to know when to turn around. In turn WR's are taught not to lift their hands or do anything to indicate they are going for the ball until the very, very last second. They've become quite good at this. When a DB turns for the ball he naturally slows down, so if his timing is off even a split second it can create space and all of a sudden a covered receiver is now open or he is called for PI. That is the reason (if I'm not mistaken) that Saban doesn't want them turning to look for the ball until the last possible second. It's not as easy as we fans make it out to be.
But for me, if the rules weren't so dang nit picky about what you can and can't do as a DB. The DB's wouldn't have to be almost perfect in execution when defending passes.