I actually disagree with most of that. Khedira at Stuttgart was more the central playmaker than a defensive powerhouse. In fact, I struggle to believe that any incarnation of Khedira is strong enough defensively to make your midfield work. I'm not a big fan of Yaya (which most probably know), but let's not kid ourselves. For most of his time at Barca, he was a quality defensive midfielder who simply offered more defensive protection than Khedira ever has. He has been a strong player, doesn't matter if he peaked in a more attacking role at a different club later.Clearly, while Muller can't find synergies with any player on the pitch. Probably because Angel di Maria is a much more intelligent player than Thomas Muller.
As someone who saw him non stop since arriving to Madrid, it's easy for me to say that the change he's done there is beyond maturing but it's build around it. He came as a rather young player and took him a while to understand the rhythm of the big boys and be able to find his control. Plus, until he moved to Arsenal he kept on being a player which, for most big games, disappear and come in and out of the games which was Real Madrid fan's biggest problem with him.
I'm not saying BuLi Ozil > BuLi Khedira, but their roles here are very different. Khedira is playing in the role he played since starting playing football, and is much more reliant on his physical attributes than his technical ones. In the same time Ozil is playing a role he could hypothetically play as CAM, although at Werder Bremen it was very very different from his role. Moreover, Ozil is being asked to do A LOT more defensively than he's used to do for any team and lacks the physical attributes to do.
So you see, I'm not saying BuLi Ozil wasn't good, but the fact is he's got this midfield trio:
Yaya out of the position and league he played his peak in.
Stankovic in a much more defensive role than he's used to and peaked in, in the club he did peak in.
Ozil in a much more withdrawn role, before his peak, and in a position he did not peak in.
while we have
Guardiola in the position he played since Cruyff first saw him in the reserve team and ordered him to move in in the club he peak in.
Khedira in the position and role he played for every team he represented, before his peak.
Sneijder one of the best midfielders in the world at his prime, in his peak club in his peak position*
*Regardless of what DK threw about Sneijder's role here - knowing Sneijder's movements he moves between receiving he ball deep, moving forward with it and drifting between the space at AM to LAM positions. He loves to roam a little to the left flank and he has all the room in the world to drift to here.
So, I'd say both midfields are incredibly lightweight.
Regarding Özil. He simply needed time to adapt to Madrid at first. He struggled to show his form from his time at Bremen for half a season before he started to improve. That initial struggle doesn't reflect in any way his form at Bremen or for Germany prior to his move to Real Madrid. I still consider his performances at the World Cup in 2010 better than anything he has done ever since.
I also think that the attempts from both sides to question the tactical suitability of the attacking players are a bit silly. Both attacking units look fine and complementary to me.