If the argument is about which player is the most exciting to watch during their peak, then I wouldn’t argue against Ronaldo/Ronaldinho being more exciting than Cristiano, although I do think the difference is minimal.
But if we are arguing which player is more exciting throughout their career, Cristiano 10 years vs Ronaldo/Ronaldinho 5-6 years of exciting play are much more impressive to me.
The problem with most people here is, they will often tend to use the current ‘boring’ version of Cristiano to compare with the peak performance of Ronaldo/Ronaldinho which they could remember, this isn’t fair at all. Ronaldo/Ronaldinho has many average/shite performances in larger part of their career which people choose to forget when doing these comparison, whereas they always brought up boring but effective version of Cristiano for comparison.
Personally, I don't put that much weight on the question how long a footballer has produced. Yes, it is very, very impressive that Cristiano has sustained his level for so long but to me that's more of a side note. There comes a point when you've seen enough of a player to judge his quality and if he falls off a cliff afterwards that doesn't change how good he used to be. He has shown this level long enough to prove that it was not just a patch of good form but actual quality.