Yes, I think that Messi, if he keeps this up, will be considered an all-time great by the time he retires.
But that doesn't mean Ronaldo won't be... I'm not going to say who will be better, because we don't know, and it's not like there can only be one all-time great remembered from each time period.
What about Best and Pelé, or Zidane and Maldini? All are considered all-time greats and will be remembered for decades to come, and yet they shared the same time period.
So to agree that Messi will be an all-time great is not to say that Ronaldo will not. It is also not saying that Messi is better; it is merely agreeing that he will be fondly remembered for a long time after he retires, much like Maradona. I think the same will happen to Ronaldo, too.