Agreed.
Ronaldo has the most amount of both goals (135) and assists (42) in the history of the European Cup/Champions League since its' introduction in 1955.
https://www.uefa.com/uefachampionsleague/history/rankings/players/goals_scored/
https://www.uefa.com/uefachampionsleague/history/rankings/players/assists/
Messi is 2nd top scorer (120) and has the 2nd most number of assists (36) in the competition's history. Ronaldo has 5 CL wins and was ever-present in each of those successful campaigns. Messi has 4 CL to his name, and only played a bit part role in the first win in 05/06 (1 goal in 6 games) whilst not making the bench in the final vs Arsenal.
https://en.wikipedia.org/wiki/2006_UEFA_Champions_League_Final#Details
Ronaldo also has won the most amount of games by any player in the competition (112). The only other player who won more than 100 matches in the Champions League is Casillas (101). This is a testament to Ronaldo's incredible consistency and longevity. The supporters of Pele and Maradona love to point out that neither Messi nor Ronaldo has scored in a knockout game of the World Cup as a measuring stick to downplay them. However, Ronaldo has 67 goals in the knockout phase of the Champions League. While Messi has 49.
The WC used to be the holy grail of football because it was a platform that gave us the opportunity to see the best players in the world facing one another. But this is not the case anymore since the injection of cash in to European club football scene in the last few decades. The European clubs now have the best players across the globe playing for them because essentially all of them fancied a move abroad to Europe due to the wages and exposure. The WC though remains a more prestigious competition for a footballer to win due to its' storied history, the fact that it is played only once every four years which makes it a more elusive prize, and the honour of winning it for your country gives them a sense of pride of being a national hero. Nonetheless, it's clear as day that the Champions League offers the highest level of quality in the modern era and hence, is the realest testament to a player's ability.
Ronaldo has scored in 3 separate CL finals, no other players has scored in more. He has scored 4 goals in Champions League final, again no one has scored as many. A tremendous amount of his goals in the competition have been crucial goals that were either equalisers or match winners. He has consistently delivered on the biggest stage of them all. So even an argument such as a flat track bully or stat padding would be nonsense. Of course, Ronaldo does not always have a stormer of a final (e.g. 08/09 vs Barcelona, 17/18 vs Liverpool) and requires a team mate to step up to help win it. That's normal because after all football is a team game and no one player is perfect throughout the entire competition. However it's important to bear in mind that Ronaldo was always highly instrumental in spearheading his team to the final in those finals that he could not replicate the same impact. They would not have even made the finals without Ronaldo to begin with.
Ronaldo dominated the Premier League during an era when the PL was at the peak of its quality. From 2006/07 to 2008/09, most of the final 4 spots in the Champions League were monopolised by English outfits
2006/07 - Milan, Liverpool, United, Chelsea
2007/08 - United, Chelsea, Barcelona, Liverpool
2008/09 - Barcelona, United, Chelsea, Arsenal
During this time, 9 out of the 12 possible Champions League semi finalists were English clubs. United x3, Chelsea x3, Liverpool x 2, Arsenal x1. While only 3 were non-English (Barca x2, Milan x1). Ronaldo then went to Spain and took little to no time to settle at a new club in a new country. During this time La Liga overtook the Premier League to become the strongest league in the world. Ronaldo and Messi were matching each other blow for blow there, with those two smashing records at an astonishing rate like no other business. Ronaldo then moved to Juventus and thus far in his 3rd season, has outscored any other player in the Serie A since his arrival. This shows that the man can certainly succeed in different countries, different climates, under different managers with different approaches and tactical set-ups. He is the most complete goal scorer I have witnessed. Long range strikes, 1 v 1, overhead bicycle kicks, calm composed finishing and fierce angled finishing from multiple angles, backheels, brilliant solo runs, headers, etc. It's a vast plethora.
Do I think that he is a better player than Messi though? No, I actually do not. They are both level in my eyes. I think Messi is the more naturally talented of the two and more complete player. However Ronaldo's mental aspects (e.g. determination, sheer athletic dedication and drive to excel) really impresses me. And I'm very sure if even I could feel this through my television screen and in the stands, then certainly this influence could inspire his team mates who are sharing the same pitch as him. In the past, I do not like him because I think he is a petulant prima donna with a huge ego. However in recent years he seems to have mellowed down a lot probably due to him maturing. And I started being less harsh on him. If my team is playing in an important game/cup final, and I could only pick between one of Ronaldo or Messi to play for my team, I would be more confident and assured of my team's chances of winning with Ronaldo. However, if given a choice to build my team around a player for a league campaign, I would be more confident of winning the title with Messi in it.