That's just silly, centerbacks do different jobs in different systems. He's good in systems where keeping the ball is the primary method of defending, he isn't in systems or games where teams see more of the ball and are more likely to go blow for blow. He's situationally a good centerback.
It seems we have now got to the point where those who want to criticise Blind are resorting to basically saying "Well he wouldn't be good for another manager or in another team", that's not a reason to not play him as a centre back and I don't think Louis van Gaal cares how he'd play for another manager, he works and so far Louis van Gaal has been right despite all the preseason criticism.
A player like Herrera is quality however in the 10 role when the manager wants a second striker not third midfielder he isn't as effective, in the holding position he isn't as effective, in this system it is therefore no surprise other players have been given the chance ahead of him and only if they don't perform (Schneiderlin and Rooney) will he get his chance. Herrera is a good player.
The reason Louis van Gaal was probably never interested in a goal keeper like Cech even if he didn't care about staying in London is because he isn't a sweeper keeper and so would struggle with that aspect of performance. I wouldn't call Cech a situationally good keeper, he's a just good keeper, it just so happens this manager wants a keeper who is very good with his feet as first choice for obvious reasons.
Jose Mourinho didn't value Juan Mata because he didn't fit his system, I wouldn't say Juan Mata is a situationally good player. Benitez was happy with him as is Louis van Gaal. And so far he has averaged a goal or assist per game!
Valdes was a top keeper but in the premier league many thought he would have struggled, I wouldn't say Valdes is situationally a good keeper.
And the list goes on.