From what I read online, PD AF cannot be precise all the time. I do not know what's the expected percentage of it being correct. I believe this is the reason to shoot multiple exposures for each sensor when testing for focus precision.

I do not know if your vision has anything to do with this - you are not focusing manually. Also, in my mind, if a camera misbehaves in the same sort with multiple lenses then only camera can be blamed for it - I would find it highly unlikely that multiple lenses would all experience same malfunction.

Alex
http://www.yermakov.net