Pep and Aragones changed Xavis role (less in how he was positioned, and more in the trust he was given, the players put around him, and the teams style overall). If they didn't arrive, Thiago would probably be seen as the greatest midfielder to come out of La Masia (Iniesta too, magically improved as a 24yo when he got to play together with Xavi full out in that different style)
Xavi was not a DM under Rijkaard, Marquez or Edmilson was. Xavi played together with Deco, who was a totally brilliant player but who played with a slightly lower success%
The talking point was wether Rijkaard could be crazy enough to play Deco, Xavi, Iniesta together or not, sometimes he did (both Iniesta and Xavi played were tried as DM)
Deco was clearly the greatest of the three in terms of reputation, before 2008.
I was obviously an outlier then, in that I rated Xavi as obviously better than Lampard in 2005. Having been very impressed with Toure in 2007, I also immediately understood Busquets was better the first couple of games I saw. I was very suspicious about Rakitic arriving to bring more verticality to the midfield, and I was right to be, even if he played very well for the most part, better than you probably give him credit for. Fabregas was a genious in a way, but too bad to play DM/CM in Barcelona. He was good as a partner to Messi up front, but a bit too slow.
Xavi was Spainish best player in 2005, way before Pep. Again, he didn't play in his favourite position (not a playmaker of the team and also as a DM) until Aragones gave him a playmaker role in the team. Pep followed that. He immediately dominated the whole world. Even before that, he was still very good. Just player like Xavi or a CM role was not appreciated like nowadays.
Iniesta already played god games vs Madrid, Milan, Arsenal in 2006.
Now in 2021, you can say Xavi was better than Lampard in 2005 but i don't know if it is true back in 2005. No edvidence.