In all likelihood, as Dias is the weaker on the ball of our centre-backs, he would always be the central defender should his partner take the ball forward. You make a good point, but if he plays with Ake, Akanji, Gvardiol, or Stones, he is more likely to be the true defender. I imagine that this would be the case with all apart from possibly Khusanov, whose athleticism makes him the natural 'last man'.Thats not the point.
Its about whatever in possession structure we have, Dias will never be the wide LCB as a preference for Pep due to the passing angles.
Lets use the left footed LB example you just said in a back 4. If the RB tucks in (Peps favourite system past few years), Then Dias in possession shifts to the centre of the back 3, with the LB now the LCB.
Alternatively, John Stones has entered midfield with Dias LCB, but the back 3 is still Dias centre with the left back again as an LCB.
This is what im saying.
This current wingback system would not work with Dias to start at LCB since no change happens to give him a proper left footer next to him, he would have to be the one passing and isnt suited for it.
I've enjoyed reading this debate.