It could be a player issue but when it's a holdover criticism from another team and you have some former players speaking out about it, then I tend to think the DC is a much bigger problem than you want to believe. For example, in the Seattle game on that one Lockett short TD, half the secondary was playing man, the other half was playing zone. On twitter, someone pointed out that part of the confusion there was because Nolan demands so many reads by the time the ball is snapped, you can often see guys confused because one guy reads one thing and another guy reads another.
And then the very next week, you saw the same thing again where half the D was playing man and half were playing zone and they gave up another big play.
Sure, you can find examples of players screwing up. Worley is a prime example. But Nolan is a bigger problem than you seemingly want to admit. And it's kind of weird, why have such loyalty to a guy that has a mixed track record as a DC?