Xavi's deep runs were very important for F9. When Messi was dropping deep he was very good at exploiting that space.
Iniesta's shooting wasn't great, had almost no power lol. But he also didn't get into clear shooting positions as a pure #10 would for example. Often very tight spaces with no space to shoot. Didn't really have that instinct either as compared to for example Coutinho who did everything he could to get into position for his usual curlers from the left.
Another interesting fact is that Kroos who is considered to have a super shot has worse goals/game than Xavi, even without considering Xavi's Qatar stint.