With defenders its not even as if you have to be 'amazing' at what you do, sometimes 2 'average' players do well together, prime example is Roger Johnson and Scott Dann for Birmingham City in 2009/10, not many goals conceded, finished 9th in their first season back in the top flight. Martin Skrtel and Mamadou Sakho are both better defenders than Dann and Johnson, but cant play together.
Next season they virtually never have both of them at the same time, get relegated, both go to new clubs, are pretty poor and their new clubs also get relegated.
Defence is all about partnerships, Arsenals best defender a few years ago was Vermaelen, but Wenger couldnt keep rotating him, Mertesacker and Koscielny, went with the latter, we're in a similar position now, Rodgers MUST decide which 2 he wants, and stick with it, for me it would be Lovren and Skrtel with Valdes as the goalie assuming he signs.