Titles matter for the Ballon D'Or and performing very well at the most important times matter too. He's the obvious winner.

As far as performing well at important times go, taking the numbers from r/barca, Messi directly won Barca 12 points in the league this season with goals scored after the 87th minute. Considering matches tons of other matches where he dragged us through to a tie or win with assists or by making plays, and he has nearly 4 times the amount of unassisted goals Ronaldo has, I'd say he has been much more decisive at important times for Barca.

We really struggled as a team this season and Messi has been instrumental in even keeping us in the running for the title. Heck, even against Juve in the first leg, when we were struggling to even get the ball past the midfield, he dropped deep and created two or three very clear goalscoring opportunities. It's unrealistic to expect Messi to win every game for Barca, Ronaldo's 'decisiveness' were in matches, very important, very big matches, nevertheless, matches where his team were handling themselves very well and he had quality service in box so he can do this thing.

I think that's why Messi clearly deserves the Ballan D'or this year. Individually, Messi has been more instrumental to the team than I have ever seen him be, and Ronaldo to just take away the award this year just because his team rose up to the occasion and he didn't particularly fuck shit up is ridiculous.