Agreed: Maradona from '80 to early '90, Ronaldo from early '90 to early '00 and Messi from mid-end '00 and on going are the three best.
No.
Maradona gave away something like 360 goals (the same number of goals, with even a better per-game ratio, of legendary strikers such as Eto'o, just to say one big name) and 300 assists playing the majority of his games as a pure 10 (see the role of Sneijder, for example) in an era where defenders and defensive methods were much harder on your legs than today; also, Maradona had way more leadership than Messi (crucial factor at the highes levels) and for a variety of reasons never really played at 100% of his physical possibilities.
Ronaldo, on the other hand, before his various problems was a machine, nobody was like him at 20 years old, he was unstoppable; still, after all of his problems, he came back at 40% of what he was before and dominated the world of football. With almost 3 years lost, and nearly 3/4 of his career played at not even half of his full potential, Ronaldo still managed to score 414 goals in 616 games.
Sorry, but Messi is not greater than Maradona and Ronaldo de Lima combined.