Man, when you compare top scorers in Europe, you compare them in their domestic leagues, not in CL. Not every player plays in CL.
I am only talking about the league, bro. If I would be comparing in all competition it would add up to this..
C.Ronaldo has played 2655 minutes in the league + 914 minutes in the CL + 510 minutes in the cup = 4079 minutes in total.
Messi has played 2613 minutes in the league + 658 minutes in the CL + 493 minutes in the cup = 3764 minutes in total
So basically, C.Ronaldo has played a couple more minutes in the league. And even though this is Messi's worst season EVER, and arguably C.Ronaldo's best season ever, Messi has only scored 3 less goals in the league, while getting 2 more assist.
If you ask me, not that bad considering how much sh*t Messi has been getting..