I agree with this, we do all see different things, I know for a fact I see things other's are not interested in. So the point you are ACTUALLY admitting to here is not that one individual is better than another (Kos V Verm) but that the pairing is far more important - which is one of the factors to take into account of when analysing this goals conceded stat - as a few of us have been telling you
I good defence is all about balance I'm in agreement with this. You yourself claimed Koscielney to have been 'magnificent' this term. I claimed that I thought Vermaelen was the better 'defender' and posted some stats that indictate he could be. Now I dont have time to go though every match of the last two seasons and work out an average for all our defenders and all our defensive pairings. The thing is, if Wenger signs Vertonghen it wont be to sit on the bench. Either Koscielney or Vermaelen will make way and I'm willing to bet my house it will be the Frenchman.