Fact is: This season Messi is doing more with his left leg, than Ronaldo is doing with his left leg, right leg, head, freekick, penalty. So it doesn't matter which player is more complete, it's how one translates them into goals and assists. Hleb uses both feet very well, but he's still one of the least performers in the squad this season.
Ronaldo was the best player last season, and Messi is the best player this season. That's all there is to it.