What we saw in this last game is an entirely different approach to the whole idea of defense and defensive play, the whole idea of "playing our own game" vs playing relative to our opponent's strengths&threat, we kept compact and disciplined through the entire game (almost), and the result was fantastic. Concluding individual stuff from that is a bit rash, I'd say.
Nacho had a very good game - perhaps his best game for us so far. I always thought Gibbs was much better, particularly defensively, but I said after the game that this is good news for us, as the difference is not so clear any more. But let's see Monreal play like this regularly before we jump the gun. He was helped by a great Sanchez-Coquelin and even Santi and Ramsey effort, and he still didn't manage to keep Navas completely out of it (and I don't think it was one of Navas' greatest games). So let's take it in perspective.
I'd still prefer Gibbs when defense is our biggest concern and when he needs to close a dangerous winger (Gibbs speed and recovery are superior). But as I said - it's no longer a big deal for me. Nacho does have his strengths, and when he plays like this the rest doesn't really matter. Plus the attacking input from Nacho is very good (and superior to Gibbs, though the latter certainly improved in that respect).