I would agree with this. However, for most people, it's not physical prowess and/or fitness which stand at the foundation of what the greatest means. But rather their talent and their ability, as well as the genius factor. Ronaldo doesn't have more ability than the likes of Messi and/or Maradona. No matter what he does this will not change. He can score as often as Messi, he can win the titles Messi wins. But he just can't do what Messi can. Ability to a point can't be trained and comes from talent. Messi/Maradona/Cruyff/Di Stefano/Pele have more talent than Ronaldo, and the gap is very clear for me when watching them.
Messi, Maradona and a select few others can put the ball where they want to. Can pick a target and deliver a perfect pass, taking into consideration multiple factors, like the wind, the spin of the ball, the pitch, the receiver's preferred foot. It's a complete mastery of the football. Ronaldo doesn't control the ball to the fullest potential. He can shoot it fine, he can head it or even do a trick from time to time, but that's about it. The rest is routine. He is not better at controlling the ball than some of his teammates for example, like Kroos, Modric or Marcelo. That can never be said about the likes of Messi, Maradona Cruyff and others.
Ronaldo can be appreciated as an example of professionalism, will to be the best, discipline to succeed at the highest level. Those are attributes that make him not only a great player, but a great sportsman, and an example for many other aspiring kids. But as the best player of all time or one of the very few? He misses some key aspects for me, which I mentioned earlier in the comment.