I don't trust anyone with over a 3 K/D. Sure there are those who have it legitimately that high, but it's still incredibly hard to believe. If you have a K/D over 20 you boosted but haven't been caught, Hell if it's over 5 you boosted. To keep a K/D that high you need to average more than 5 kills per death. At that high any extra death exponentially decreases you ratio. Any extra death. Just one more death than you normally have will cut it down quickly. With Ghosts' terrible spawns there's no way he avoids stupid deaths every game. So don't believe in this K/D.
As far a general stat this is a timeless debate. In short, a K/D is what you make of it. It's only as important as you want it to be. Each player has their own perspective on it. I look at my K/D like a barometer; it tells me how I'm doing for that week. If it goes up I'm doing something right. But, if it goes down I need to make some changes. I take it as it is and I don't try to manipulate it. Recently my K/D has been going down. I stop to think why this is. Most of the time it's pretty obvious. I've been playing solo a lot and I'm also playing more DOM than TDM so I'm sticking my neck out there more than usual.