Are you serious? CL says hi. And not only that, but if we're unlucky with injuries again, I can see a cb pair of Bartra and Bagnack playing. Do you really think that's good enough? Puyol, Pique, Masch and Bartra?
But that's the same with any team. If Hummels and Subotic get injured Dortmund will struggle. If Ramos and Varane get injured RM will struggle. How many teams are there with more than 2 or 3 high quality CBs? Bayern and Chelsea maybe? Chelsea haven't been that good recently, and Bayern would have a problem if Ribery and Robben both got injured.
As well as our best attacking record ever. Differing tactics would change the balance more than a new player(Thiago Silva excepted maybe).It was also enough to have our worst defensive record in 20+ years?