No, certainly not.
See just because I add 'certainly' to my opinion it doesn't make it any more than just that.
You think Chelsea would have sold their best center back? You're a bit foolish if you do....he isn't worth twenty million, nevermind the ridiculous fee he's gone for.
He has great anticipation and is good on the ball, two attributes that are not needed at Chelsea because they play with 10 defenders anyway. Cahill and Terry are decent defenders, nothing more than that, but people don't notice because, as stated, Chelsea play with 10 defenders. They would be beyond terrible at a team like Barça.
Just because Luiz makes mistakes doesn't mean he's worse than those two, he has a lot more going for him, things that those old-fashioned defenders can't even dream of and that are a requirement for a defender in modern football.
By the way, if Chelsea got an offer even half of what they sold Luiz, they would take the money and run. It's also about practicality, if you don't necessarily need a player and you can sell him for 60 million, you do it. With that kind of money, they can buy a better defender than Luiz, Cahill and Terry combined, or several talents with world class potential.