I wouldn't exactly call the 3rd debater an imbecile. He has a somewhat valid point in my opinion. The truly legendary players like Pelé, Ronaldo, and Ronaldinho all achieved something with the Brazilian national team. They won at least one trophy if I'm not mistaken.
Messi is absolutely amazing on the field for Barcelona. I think his success is partially due to the company that the team keeps around him. He has world class players surrounding him and making sure he shines. Hell, they even play a strategy that seems to work towards his strengths.
The Argentinean national team on the other hand aren't equipped with arguably the best players in the world at every single position like Barcelona. The national team also doesn't use a style of play that makes Messi the focal point. Other players use their call up to the national team as a chance to show what they've got. Add that to the fact that he doesn't play qualifiers or many friendlies with his national teammates. Your end result is a struggling player who can't do anything right. Except for a moment of individual brilliance here and there.