Well, what I think is that wingmen should always grind as tight as possible, and center is sort of a "last resort", although it obviously should try to kill players nearby, which are most likely the ones trying to get through.
This "#1 covers center" seems to happen because both #2 and #3 usually double grind, and end up with a poor one. Even funnier is that some times players doing so don't care much about it, and keep doing a light grind, leaving center the job of covering it.
Of course the defense should protect center as well

So, what do you think?