Philosophically he places the premium on tackling at CB, he really doesn't care about coverage & technique, because his Defense is all about creating havoc plays upfront & getting TFL's, he sacrifices elite coverage for the hope of causing 2/3rd & longs. Everything is predicated on getting the offense behind schedule by disrupting rhythm upfront, the backend is all about the Safeties, he puts almost all of the responsibility on the S's in their coverage shells.
That's the crux of the issue, Manny doesn't really value high level CB play, he thinks it's inconsequential to the success of his Defense, but he's miscalculated that in this era of football you really can't survive without having great corners.
Coverage skills & footwork reigns supreme, yes tackling & setting the edge is important as well, but if you don't have physical cover corners who can't win the leverage battle & transition in phase to make plays on the ball you'll be shît out of luck.