Xavi said recently that Lucho took the physical training to another level in Barcelona and you can see that when the team plays at it's best. Not many people are taking into perspective how much the midfield duo of Rakitic and Iniesta have improved in their defensive capabilities. Under Martino and Roura (I refuse to say Tito, he didn't have time to leave his mark on the team) the 2 CM did an awful work in defense, it was just Busquets against the world with a little help from Alves when he had a good day, Iniesta has vastly improved his tactical awareness and even in his 30's he runs, tackles and covers space better than ever. Rakitic had a lot of problems in Sevilla when he wasn't playing as a 10, some even said that he wasn't able to hold a midfield as a CM and that signing him Barcelona would lack deffensive effort, obviusly they were wrong
Pep's work has some myth now that some years have passed from his Barcelona era, he had a player similar to Rakitic in Keita (better at destroying and heading, worse creating and at long passes) that played 40+ games every season with him, I may be biased but I'd say that Pep had a better team than Luis Enrique (Midfield was superior with prime Xavi/Iniesta, Busquets, Toure, Keita, Hleb) and a front three with Messi, Henry and Eto'o wasn't a joke. The difference in the defense is even greater, as Guardiola had Abidal, Marquez, Pique, Alves (THE Alves, not the current one) Puyol and Milito sometimes. So even when Pep's team had the control of the game more than this Barcelona and could defend with the ball, Alves - Puyol - Pique/Marquez - Abidal was way better than the Alves - Pique - Mascherano - Alba that Lucho has played (when the whole defense is fit, one injury and all goes into shambles)
But the greatest achievement Lucho has done so far is being able to keep winning and dominating while transitioning from a player that marked a era in Barcelona and Spain, Xavi was the catalyst of this team for more than a decade and everyone should've known that once Xavi was no longer our midfielder no one could replicate his role and hence the team would have to look for other ways to play and keep winning without throwing out the last 30 years legacy, now there's a balance between the possession centered play that only Xavi could achieve and the fast, direct football that some players need in order to shine while convering our flaws
I mean, Iniesta is doing his best to replace Xavi but you can see here...
the difference between him and Xavi, to do what Xavi did, Andres needs twice the field, time and stamina. I don't think a lot of managers could replace Xavi in a team and keep winning, even with the front 3 the team could break apart easily, as we see year after year with Real Madrid