I'm not sure about that. Argentina have some really good players who I think sometimes get intimidated by Messi and just let him carry the load. I know when he doesn't play their performance suffers but I wonder how they would do long term if he wasn't playing. Portugal on the other hand (for the most part) are just not very good without Ronaldo. Sure they can play above themselves as they did in the Euro final but when they won it, it was more of a surprise than anything else.
i think Argentina's biggest problem, even if we leave out Messi is that they don't have competent creativity in the midfield.
they have forwards who are easily among the best, if not the best in their respective leagues.
Higuian, Icardi, Aguero, Dybala and a winger Di Maria, at one point of time have all been the best player in their position in the league or even world, bar Messi/Ronaldo.
Apart from Icardi, all played in teams who had excellent midfields, but when it comes to NT, they don't have a decent midfield for chance generation.
and I agree, downplaying Cristiano's role in their Euro win or his importance in NT is silly, but that is part and parcel of the stupid fan war, and when people use that win to say Ronaldo has been better than Messi NT scenario, it bring some people to downplay his Euro performance.
And it is not one side issue as people on the other side are quick to downplay Messi's role in WC run, because he did not scored in KO stage, when the truth is the only below average match he had in WC was against Holland, even though he did created chances which should have been buried to avoid the penalties.
Now it may look funny and silly, but it was true they struggled to beat the likes of Bosnia, Switzerland and even fecking Iran, and required magic moments from Messi to win.
People have this notion that Messi becomes average player with NT, while truth is Messi issue in NT is just that he does not match the goal count of Barcelona's self.
Other than goal, if you go by his other aspects like, dribbling, chance creation and assists, it is same. In WC14 and all three Copas(2011,2015,2016), he was leading in chance creation and among the top dribblers. Just like he is with Barcelona.
If Messi plays good, Argentina wins, if he struggles to bring magic, they lose. And that over-reliance on Messi is a bad thing as you pointed, and even their coach was claiming few days back it was Messi's team, maybe it is to inspire players to win WC for Messi, still a wrong attitude.
And I have a funny belief that if Argentina wants to win the WC, they would need a major shady incident, bring the true Argentine stereotypical attitude of cynical, cry baby and cheating attitude. I mean both of their WC wins had two big shady incidents(sixer against Peru in 1978 and 1986, the hand of god). A Messi dive to win penalty and send off a opposition player, is what they are missing.