That’s abit of understatement, as Ronaldo has been the key player (and top scorer of tournament) in all his 5 CL win, whereas Messi only feature heavily in 3 of those (the other 1 of them being a bit part player only)
But this is the kind of tenuous argument that you have to make.
Messi has been absolutely the key factor in Barcelona's dominance of Spanish domestic football, which is 80% of the matches that they play in the average season. That is the bread and butter of every team in every country. In fact, considering his passing, dribbling, free-kick, assists and goals statistics, let alone all of the brilliant things he does that don't necessarily contribute to these categories, it was arguably Messi's best ever domestic season. That was in a team as well that was expected to struggle after they were battered in the Spanish Supercopa.
Whereas Ronaldo and Real Madrid had a disastrous league season, which meant that they had to completely concentrate on the Champions League. They didn't have any choice because they were completely out of the running for the league by Christmas. This basically comes down to a few matches, as both Real and Barca are guaranteed to reach the knockout stages every year. Messi was brilliant in both legs against Chelsea, was instrumental in the 4-1 win over Roma. So he basically had one indifferent game, Barcelona had a nightmare at the back, and according to you that then undoes everything he's done in the rest of the season.
And Ronaldo then gets to take credit for things that he hasn't even achieved. He didn't single-handedly win the Champions League, in fact he's nowhere hear as important to Real as Messi is to Barcelona. What you are effectively asserting is that because Gareth Bale scored an overhead kick against Liverpool, Ronaldo is a better player than Messi. Even though Messi has outperformed Ronaldo virtually all season (again), and been much the better player in the El Clasico games (again).
Even when they've met in the Champions League, here is what has happened:
Barcelona 2-0 Manchester United - Messi scored, Ronaldo did not score.
Real Madrid 0-2 Barcelona - Messi scored twice, including one of his best ever goals, Ronaldo did not score.
Barcelona 1-1 Real Madrid - neither of them scored.
I don't even think Ronaldo has performed better than Messi in the Champions League. Messi has turned in numerous truly standout performances of individual brilliance (see his four goals against Arsenal, the Real game at the Bernabeu, the final against Man Utd, the Bayern Munich semi-final, five against Bayer Leverkusen, turning the tie around against AC Milan) whereas Ronaldo has been an extremely consistent and effective forward, but less instrumental in what Real Madrid do.
It's much the same with international football, where somehow the people who bizarrely want to believe that Ronaldo is a better footballer than Messi (laughable, in my opinion) will claim that he's won an international medal, therefore he's better. When, in reality, Messi's performances in the Copa America were clearly far better than Ronaldo's in the Euros. This is the problem with comparing individuals in a team game, but you surely have to look at what the players do on the actual pitch, rather than what they've won.
And another thing is that people always cite goals. As I've said numerous times, Messi does not play as a forward. Messi is scoring 45 goals per season as a number 10, and also leading La Liga in passing, dribbles, assists and free-kick goals. Ronaldo is a pure poacher now, who does almost nothing else other than score from close range. He's extremely good at it. But he could be replaced by Lewandowski, Suarez, Kane, and probably several other strikers, and you would barely notice the difference, if at all. Messi cannot be replaced, certainly not at present. One day, Neymar is going to go past him as Messi gets older, but that certainly hasn't happened yet.
I really don't know why this is difficult for people to understand. But I used to believe that most people who watched football:
(a) were capable of basic logic and reasoning;
(b) basically understood what was happening on a football pitch.
Then someone invented the Internet.