I don't know how anyone can follow Messi's career over the course of this season and decide that he hasn't performed in crucial games. Or, at least, hasn't performed as well as Ronaldo in crucial games. Even this supposed low-point to his season - against Chelsea - featured no worse a performance in the first leg than Ronaldo put in against Bayern in Munich.
As Brwned already pointed out if you want to talk about attacking footballers at Madrid who are really turning it on at the business end of the CL then Benzema is arguably out-performing him. Which, in part, explains why Barca failed to beat Chelsea. The fact that nobody else at Barca is stepping up to score the goals instead, when he's not quite on his game.
Err where did I say Messi has not performed in big matches throughout his career? I am strictly talking about this season.
Besides it is a combination of your from throughout a season and your contribution in the big matches at the end of it.
I have no idea why people have their knickers in twist. Messi is still the BPITW but it is very much conceivable that he won't win the golden ball now if Ronaldo performs in some of the matches he has to look forward to for Real and Portugal. That is all there is to it.