I think the same, even if Messi had a drop on his performance due to his age or an injury, if I was the coach of the Argentinian national team and I was given the choice between bringing a player which may not even play or Messi, I will pick Messi, as not only he could always change a game with a single play of his, but when we add the leadership he has, he could easily help his teammates and give them some advice even if he was not on the field.
The case with Argentina is different from that of Portugal. Argentina has an enormous pool of talented players, and already youngsters such as Julián Álvarez, Alexis Mac Allister and Enzo Fernández are performing well at the international level. The case with Portugal is different. They were always a one-man army led by Ronaldo and once he retires he will leave behind a huge vacuum that none of the younger players will be able to fill. They have a few youngsters like João Félix and Rafael Leão. But I have found these players to be very inconsistent.