From a pure subjective standpoint I'd concur but it's hard to make a claim for that using numbers. In the end Messi broke every record possible and his overall skillset might be even more complete than Ronaldo's was. The letter still edges it for me though because he had that power and tenacity that you rarely get to see these days and comparable skill and vision to Messi or Dinho. He had a very special aura. As soon as he had the ball it felt like his opponents were bricking it, comparable to what Messi does to today's opposition. The difference being that the defenders of the 90's and early 00's had a lot more freedom in terms of making "contact" with the striker. Most of the time even the greatest defenders of their generation like Nesta, Maldini, Costacurta, Cannavaro or Thuram - a quality of defenders today's game is lacking - had no choice but to chop Ronaldo down to stop him. Messi gets his fair share of fouls as well but these days heavy contact is less frequent and less extreme because yellows and reds are easily handed out to protect the players. I think that's a good thing actually. Less physicality makes for a more fluid, faster and asthetically pleasing game. Football evolved in that regard and since it got easier on the eye it appeals to an even wider audience, which generates more money. The state of the pitches improved as well. The balls used today are a fair bit lighter and travel faster than those used during the 90's.
Since both players played in different eras and leagues it's very hard to make a fair comparison. One could take into consideration that during the four seasons Ronaldo played up to his knee injury (from age 18 to 21) he produced better numbers (a goal every 102 min) than Messi (a goal every 139 min) did at the same age, and that Messi's sick stats came at the same time he had players like Iniesta, Xavi, Alves, Puyol, Eto'o, Henry, Ibrahimovic (each a legend of the game in their own right) etc. beside him at their respective peaks, and Barcelona completely dominated Club Football unlike any team did during the 40 years prior. Of course they wouldn't have been just as dominant without Messi, but it's hard to imagine him repeating those feats under different circumstances in a less dominant side and in an era where defenders would have just physically abused him and got off with a warning.
I started watching football more frequently between 1988 and 1990 and the first players to really fascinate me were Van Basten, Bergkamp and Matthäus, later Romario, Rivaldo, Ronaldo, Zidane and Ronaldinho. They were all very special players and among those Ronaldo still managed to stand out for me. In the end its probably more a thing of personal preference, but at his absolute best Ronaldo was pretty much unstoppable, even with his shirt being pulled and his legs being kicked he just plowed through back lines made of world class defenders. As much as I try to imagine it I just don't see Messi being able to do the same... to play in a lesser side and still harrass defenders constantly despite them being allowed to push him around... I just don't see it. I could be wrong though.
It's not that Ronaldo didn't dominate - it's just that the top talent during that time was pretty evenly spread among a wide variety of clubs and no club dominated to the extent the current European Superclubs like Barca, Madrid and Bayern do. And we don't talk about Ronaldo's time at Real and Milan here. His knees were shot long before he arrived at those clubs. Basically from '98/'99 onward his body was done.