They aren't shit. They are great defenders. But none of them are without weaknesses. For once I partly agree with Arcspace: They would walk into most teams' back line. They are, however, looking even better than they are, as the 3 CB system helps them disguise their weaknesses.
Look at our Dier: As a CB he's always looked a bit dodgy, a bit lacking on awareness and concentration. That has mostly been invisible in the back trio (except for the Hazard header in the Chelsea game, that was awful).
A Norwegian pundit (Hangeland) recently set up the "best team" picked from the squads of Liverpool and United, ahead of the game tomorrow. The defense was:
Valencia, Matip, Jones, Milner
Seeing that, does anyone still think the Chelsea defenders are bad?