I don't know what you want more from a 2nd round Rookie CB.
In a league where you have to play WR on every snap that you face probably once on every second team in college you can't expect a Rookie CB to be a star, look PP21 took 3 seasons to start to be a shut down CB, Sherman needed 3 years as well, hence only a handfull of CB make it in the first two years and most of them are never shut down or star CB in all there career.
Murphy showed he can be a good to great nickle CB and maybe a okay to really good #2 that is more that is everything you can hope for a 2nd rounder.
Kirk on the other hand, was disapointing this season to say the least, but again, his third O in as many years in the NFL.