I'll have a go at the 12 off the top of my head:
smalling, cahill (it seems Roy believes so)
Terry (considered by many to be the best in the division irrespective of his personality)
Koscielny, Mangala and Sakho (all have more caps than Laporte)
Kompany, Vertonghen, Alderweld
Arguably Jagielka and the Argentinian at Everton (when Stones was kept out of the team)
Denayer (according to the masses on here)
Morgan (was in PFA team of the year)
That's 13 but Denayer doesn't count as he's not yet played in the premier league..
PS I am not actually suggesting that Stones or Laporte are good or bad buys. It is clear that neither are the finished article as there are others picked ahead of them at club or international level, but somebody has to make a judgement on whether they believe they will evolve into Bobby Moore or David Luiz. I suspect the margins between these different outcomes are very fine.