You have totally and utterly misunderstood the concept
It's not all or nothing, it's not that these players individual are nothing but great within the team
This is what is meant.... try to keep up this time
Each individual player is a very good player, they are all very talented and would perform well in any team BUT together they are on another level.... not ONE of those players except Villa, Abidal & Puyol would be as great as they are in any other team......
Xavi would not attempt/complete as many passes or get the ball as much as he does as other teams won't work like Barca, they won't keep the ball for 70% of the game. Other teams can't do that as they don't have the proper players. Put Xavi in Chelsea or Utd or Inter and he would suffer. Just like he was prior Pep..... Ordinary...... As I've told you before it took the perfect circumstances for Xavi to succeed (same goes for the Spanish National team, imagine him in Portugal, Germany etc).... Best Midfielder of all time? Now that's a joke....
And the same can be said of Pique, Valdes, Alves, Busquets, Iniesta, Messi & Pedro..... not that these are bad players, that's not the point, they are all great players but together are all at another level. Individually these players are on the same level as Real Madrids players, but together they are more effective.
But Puyol and Villa can play anywhere as be as good. Villa was much better at Valencia and Puyol, unlike Xavi, shone before Pep. He hasn't changed, he's always been that strong centre back. Abidal just goes about his business, he's a player you don't notice, like Arbeloa, reliable, does not have a bad game nor does he impress and stand out....
All the other players benefit from the team.... which is a great thing....
Pep is managing a great team, so yes it does make him look better and yes he did impact this team and we can argue that he is the main reason, that if another coach took over Barca wouldn't be here etc but we can't say that. Pep made subtle changes, nothing drastic, which were started by Cruyff.
But Barca is suited to Pep better than any other team. Will Pep get another team to play as well as Barca and win as many trophies? No.....
So right now Barca have the perfect team, they have the players and the coach who understand every aspect, and together they are superb. Everywhere else, such as Messi in Argentina, they are just great players, and great players don't win you trophies, great teams do..... and that's what Barca is... a great team....
EDIT
Exactly.... Xavi was good... but not this good
Messi would be great, I agree with that, but he wouldn't be at this level, like you said his level of performance would drop....
I never said those players were not good, just not as great as they are in this system