His hesitation to play trough balls cant be due to his "decline". Him getting tired more easily, not being able to do as much defensive work or be a passing option everywhere can be due to his old age, but one does not simply forget how to play a trough ball.
Tata should have a talk with him.
It looks like we changed the way we play; Messi drops deeper, our wingers cut in more and Xavi almost plays double pivot with Busi - that's why he is further away from the having the chance of delivering the final ball, the 'killer' pass. When we play our best team, it usually looks like this:
-------Ney/Pedro-------------------Alexis-----------
-----------------------------Messi--------------------
------------------Iniesta/Cesc-------------Alves---
--Alba------------Busi------Xavi---------------------
------------------Masch----Pique--------------------
In this system Xavi is a little further up the pitch and maybe doesn't have as much defensive duties as Busi, but Xavi drops veeeery deep when we start our play from Valdez - many times deeper than Busi. Another Change I've seen is that our CB's are instructed to do more forward runs, many times our opposition have our midfield man-marked which gives our CB's who are very technical (at least Piquebauer and Bartra) the opportunity to start attacks by advancing with the ball. I kind of like this strategy, many teams knew before (like against Bayern) that Busi/Xavi is spine of our team and marked them out of the games. This makes our team a little bit more unpredictable, but unfortunately we lose Xavi's qualities up front - but they are compensated with Messi's latest strategy. But maybe I'm wrong?