Just playing devils advocate, what if it was the other way around?
Those 3 allowed Messi to do his business. They proved it on the international stage.
Can midfielders be GOATS?
The GOAT stuff it's very very silly and I will say it 4000 times if necessary...
The thing with GOAT it's the term itself, Greatest of ALL TIME...do you realize that this means and randonmly naming being
clearly "better" on individual basis (not trophies obtained) than: Falcao, Kaka, Socrates, Laudrup, Overath, The Kaiser, Charlton, Di Stefano, Gullit, Rikjaard, Redondo, Lothar, Sarosi, Baggio, Didi, Labruna, etc etc etc even more old farts like Monti, Andrade and so on. Do you realize that even a couple of years before Pep in Barca fellas like Deco, Ronaldinho and cia made very difficult for Xavi and Iniesta to actually be starters and that for Rikjaard that version of those days from Xavi, wasn't precisly his cup of tea and Rikjaard knows a thing or two about the midfield role even if he could have used them more and Van Gall used them better.
So regarding "the other way around", what would have happen if Xavi actually left Barca prior to Pep's period? he was really really fecking close. The scenario as talented as he was, in ending in a great Valeron or De La Peña if he went to a lesser club, was more possible than actually ending winning everything that he won in Barca and be named by some
the best midfielder ever (sthg that as much as I like him, it's too much, even in comparison with his fellow spanniard maestro Luis Suarez).
Many times being from the house, being from the country of the League (all around the world, not only in Spain and maybe even more in Barca if the player in question is Catalan) helps to not be shown the boot to a way lesser team when you are not entirely clicking, it happened even with the extraordinary Pirlo.
So there is quite a big element of being from the house that helped not few players around the world to keep a float their carrers in their higher echelon (no matter how talented they were and in some bad cases with no talent like Oleguer). If you arrive as the new Turk sensation in teams like Man Utd, Barca, Real, Inter, Milan you better do it fast and big to keep your boat afloat to later actually do it grand.
BTW Xavi and Busquets (this lad even more in my opinion in terms of his game, not his leadership) are the ones that are trully Barca boys, not even Iniesta is a true Barca boy in his style and atributes.
Messi and Iniesta have other atributes and capabilities that can give them more tools to adapt to diff coaches and scenarios than the other two brilliant mofos. I have a very soft spot for Busi and specially Iniesta, I love them, yet the whole
they made Messi was more of a Chiringuito stuff than anything.
For years it was said that Messi was a "system player", one of the most silly things ever said, just in order to feed the agenda of the press against him in order to demerit his talent. Sometimes I wish he played for Real, they are more clever in how to elevate their main figures (and has a more powerful reach on every sense), than Barca's self destruct tendency on every order.
That quartet cliked like angels and fed themselves in a very generous way, that it's the main thing of why the click so well. Their egos, that they had, recognized what everyone brought to the table and helped each other, but individually Iniesta and Messi would have had it easier (never 100% secure) to work wonders on any fecking club without "buts" from any type of coach. Busi and Xavi, SADLY, need more of coaches that get what they bring and understand what they need to make them feel and play better, since make them better, makes a better team overall.
One of the best examples that many here will remember was the Final in 2011. United started really really well, the Barca mid was struggling at first with the high pace back and forth situation, the match needed some pause and an extra man. Xavi called for Messi to drop and even a single play like that high pressure from Vidic to Messi ending in that glorius nutmegg made United hesitate to keep a high line, suddenly there were 4 in the mid all the time and those four were fellas that have telepathic understanding and technically as sound as you can get, the rest is history.