I disagree. Lionel Messi performance in the national team does not come close to his brilliance when he plays for Barcelona. I don't think he has won a trophy with his national team. Argentina is strong without Messi, having Messi in the game may be unfavorable for them. Portugal doesn't have the best squad but they have Christiano Ronaldo. He makes all the difference. I don't think Portugal will win the world cup, but I believe they can beat a Messi Argentina anytime.
I understand what you are saying and would partially agree. Messi is more comfortable with Barca and his bonding with other Argentine players is not that great. But this is going to be his last world cup in all probability, and I am sure that he will not create any unwanted ego issues. After all, Messi want to be a part of the world cup winning squad. Back in 2014, Argentina reached the final, but that was the closest they had since 1986.