In my opinion, this is a biased statement - Xavi and Iniesta made the greatest contribution to the team. If you remember Xavi and Iniesta won the 2008 European Championship, then the 2010 World Championship and then again the 2012 European Championship - the greatest achievement. They did it without Messi, and without them, Messi himself failed at the 2010 World Cup and then at the 2011 America's Cup.
If you are solely talking about the 2010 WC, I have to say that compare the teams Spain and Argentina had. Yes, Argentina were a decent team back then but Spain National. the team was just far better. They had Iniesta, Xavi, Ramos, Casillas, and also the legendary David Villa and Fernando Torres.
So we should not be comparing the international achievements here.
If you wanna do so, look at what impact Messi had with this shit-current Argentian team. Without Messi, they are barely able to do anything. So, I could be biased but Messi has one of the most influence on both Barca and Argentina.
But isn't it logical to compare Messi's success apart from Barcelona? In the 2010 World Cup, he was bad, not because the national team played badly, but because he himself played badly. At the same time, Xavi and Iniesta played equally well both in Barcelona and in the national team. Isn't there a pattern to be seen here?