It's still a recruitment issue because it seems pretty clear for a long time we having being getting defenders who the manager seemingly has no idea how to fit in their system. Like someone pointed out Wood was signed for Martin's system yet it didn't work at all at he was immediately removed from the first 11. A amanger can't magically make someone fit into their style or the team, it's for recruitment to make the right calls in bringing in the right players that fit. It seemed to happen under Martin a fair bit that we would get players that he seemingly had to idea what to do with.
If you're getting 12 Center backs in 6/7 years and not a single one can break into the first team, that is not solely a manager problem, you're clearly buying the wrong players. But I do agree that once they are there it becomes a manager problem and it is very concerning that we can't seem to squeeze any potential out of these players.
Again I will stress that it comes down to a culture we have cultivated where players come in expecting to be moved off again within a year or 2 after a period of good form. That's where the arrogance and lack of personality comes from these players, no one we have seems to want to play for our club and make our club good. They want to come in, get some form and get their move on.