I don't think them two, as a pair, contributed to a bad form as much as some people would have you believe. Our midfield is notoriously terrible at defending from the front, we invite a lot of pressure and confusion in our defense through bad decisions of our midfield. Can't blame the attackers for it, it's their job to go at oponnents and risk losing the ball that way but we don't recover it quick enough and often there are poor passes that invite a lot of pressure. It's hard to judge two center backs in such a system, you can give us van Dijk and whoever else is the flawor of the month to be our 2 CB's, if we didn't fix the midfield they would look average or poor as well.