I don't see anyone saying he's ideal at CB apart from a few ageists. He's a CM, always has been, always will be, and he'd still be considerably better there than Dunjogin or the poor man's Spanish Gareth Barry. Pep's a stubborn, obsessed bastard and it's those qualities that has seen the season pan out the way it has.
It was only last season where he was considered the best CM in the Prem. If he doesn't put in that performance last season against a rampant Dippers side at the Etihad coming back from injury, with the team coming off poor form, we don't win the title. You don't lose your legs between then and the start of a new season.
Let's not kid ourselves though - he is the second best CB in this squad. That's testament to his all round ability as a player and the drop off/decline in both Stones and Otamendi. I have faith in Stones to come good, and see this as an aberration. Otters needs to be sold, but before that, the gaping hold that Fern's removal from midfield has caused needs to be addressed because Pep has made a massive mistake thinking you can play a Busquets type as your holding player and succeed in the Prem.