I also think, that Argentina is not the strongest team of the remaining for nations that are still in this world cup. For me France is the big favorite. As you already said, Croatia is a very strong team too. They have a lot of quality in their squad and they also play with a lot of passion and conviction. Their greatest strength in my opinion, however, is that they are very good at defending and even if the opponent is making massive pressure towards their goal then the croatians still remain calm and are always defending well.
If Argentina wants to go through tonight, then they will need more than just Messi. They will need a good team performance.
Croatia and Morocco are the teams that rely on defense, while Argentina and France are representatives of the attacking style, so we have to see who will be stronger. I think that Croatia and Agrantina are very equal teams, if in the match with Brazil, Brazil was the clear favorite, but in this match the chances are equal. the Croats can score today, but can the Argentines score against the Hovats today?
I would not say that Croatia prefers to play defense, they scored 4 matches goals in this championship, so if necessary, in principle they can play a sharp attacking soccer, just a team of age and so they save strength, knowing that the "second breath" of Modric may not open.
Therefore, the Croats play pragmatic soccer, but with the same Brazilians they applied high pressure, trying to keep the Brazilian team away from their penalty area.
Argentina is clearly not weaker than Brazil and they can and do score. Maybe it's even good that Saudi Arabia beat Argentina in the beginning and they had to give all in every game, remembering how the game with Saudi Arabia ended.