Argentina is actually still a very strong team. They are still dependent on Messi but they also still have a lot of other strong players. I wonder how Argentina will play. Would they then return to play for Messi as Barcelona did for years before his departure? Maybe you should give those players a little more freedom. They can beat anyone on paper at this tournament. In 2014 they were already 2nd in the world, but they could also have become world champions. They are not among the top favorites, but they are not among the outsiders either. I think they are just at the sub top behind 4-5 countries.
Argentina is a great time with a fantastic player. But Brazil is even better as an overall team.
I'm sure Argentina will end up doing a great job in this world cup, but it will all depend on Messi to see if they actually end up winning the tournament. It would be an epic end to his career.
On the flip side, if Argentina doesn't win the world cup, Messi will end up retiring without ever winning the world cup, something that Maradona did.