50 goals in 107 games (31 in his last 40), a world cup golden ball, three international finals - oh and an olympic gold medal... if thats him being half the player then I assume your just pointing out how amazing he us at club level because internationally thats pretty impressive
Also worth noting that Argentina have basically had 5 great attacking players over the last 6-10 years and 3 are 9s in Tevez, Higuain, and Aguero (other being Di Maria) and the latter 2 are really not known for their passing, so Messi has basically been more of a creator than a goal scorer.
Argentina threw away their chances of winning in 2010 by appointing Maradona and not taking Zanetti or Cambiasso. In 2014, they might well have won it if Tevez was the 9 off the bench instead of the mediocre Palacio. It's not Messi's fault he comes from a country with a dysfunctional football (and political) bureaucracy.
I'm only old enough to have seen Rivaldo, Fat Ronaldo, Zidane, Ronaldinho and Cristiano in terms of true attacking greats, but I think Messi is comfortably better than each of them. He's the goalscorer the Ronaldos were, while being the passer Zidane was, the dribbler Ronaldinho was (less flashy, but as effective until he started to slow down a tad this past year or so).
Over the last 10 years, only Ozil has been comparable as a consistently devastating final 3rd passer as Messi. I guess there's a case for Totti but I don't think he's been quite as good as those 2 at it. Cesc and Sneijder had incredible peaks in this regard, probably about 2-3 years, when they were comparable, but nowhere near the longevity. Nobody else comes to mind as close to the same sort of end product as a passer. Maybe if Xavi, Pirlo or Modric were 10s and played closer to goal, but they didn't.
I have no idea how good Maradona was. But I've been watching Messi and Cristiano the whole time and there's no comparison for me. The only argument I can really see for Cristiano being his equal is that he's as good a goalscorer and against really packed in, low block defences it's a real positive that he's such an incredible aerial threat. But Giroud and Bergkamp score a similar number of goals and you never hear Arsenal fans argue about who was better. That sounds like trolling but I really don't think it is.
Can someone be as good as Messi in the future? Sure. But I wouldn't bet on it happening particularly soon. Over the next 20-30 years, though someone should emerge. Pele peaked in the 1960s, Maradona in the 1980s and Messi in the early 2010s. So, sometime in the 2030s or 2040s we might see another. This sample size is too small to really be predictive and for all i know I'd be here arguing that Beckenbauer, Di Stefano or Cruyff were as good or better than one of those 3 guys if I was around for their careers, too.