I think we should focus on players like Kara Mbodji, De Vrij or Keane at most.
We're not getting close to VVD or Koulibaly.
I am not sure that, besides the Man United match, that you have watched Kara a lot. It is correct that atm he is playing well, but look a bit further back.
Positives. He has very good strength, good header and good elbows and a lot of confidence.
His previous trainer was happy that he left Genk because he was a toxic influence in the dressing room (he thinks he is the king; his words not mine). Everywhere he goes he has issues with the fans. He is one of those defenders that is prone to making mistakes (bad passes to the keeper, lacking concentration ...), his most recent idiocy was 16/04 in the game against Oostende - it's on youtube I think. He has an issue with his knee, for which he's supposed to have an operation but they have been postponing it for two years. He has no speed, as a result he constantly has to make stupid errors.
Oh and a lot of the time he's physically present on the field but his brains are absent. This all happened in one match:
http://sporza.be/cm/sporza/videozone/programmas/extratime/2.49405?video=1.2948030 . Got to love free-kicks in the feet of the attacker; or even better who doesn't like CB's who try to dribble attackers and lose the ball. His nickname somewhat ironically is King Kara.
Besides this, he's an excellent player and who knows maybe he'll suddenly start playing better in the PL.