Well yeah exactly. Obviously a big guy without the required technical skills would also be problematic. (particularly for a team like ours where defenders are required to play out of the back) In an ideal World you want someone like Kompany, Vidic, Hummels who has the physical attributes as well as good technical skills. I would be interested to see how Mertesacker does given a run of games. (His lack of pace does worry me though but he has alot of good attributes)
The only think I will say about Kompany, Vidic, Hummels etc (Diaby) is those guys that are fast, big and heavy, do get injured a lot and seem to have a short shelf life. That is why I am wondering how well Kompany will hold up. Its like Ronaldo (the big Brazilian one), it takes a LOT of very hard work to stay fit and, at the top of your game when you are that size and after you have won a title it is even harder, as your motivation is just a little less.