I agree with you. Argentina are considerably stronger than Croatia in attacking and defense department. But Croatia played a game that looked like they were targeting from the start of the match that they would take the match to extra time. They also play the mind game well during the match. I don't think Argentina will want this match to go to extra time anyway, because they will never want to take the pressure of penalty shoot out after going into extra time.
In the last game, Croatia was really strong when they beat Brazil. Their midfielder was indeed able to make Brazil fail to build attacks properly because Croatia tends to dominate the midfield compared to Brazil. Midfield dominance in that game will be crucial, and Croatia may do the same against Argentina.
Argentina has many advantages over Croatia, but certainly has some weaknesses. Argentina has a tendency to get emotional quickly so it will be very bad when the game with high tension. Their quarter-final match was really bad, the game was so rough even though in the end they won the match. It is true that Argentina is expected to reach the final this time, however I will be looking forward to the two teams actually fighting for a ticket.