They were always one of the favorites and strikers are usually the most valuable players. They had decent teams in all World Cups though, and man for man, they were always (except on this one) better than Portugal.they had a good side in the last Euros and the last world cup too. And they won in 2016.
Argentina haven't always had the best side either. They've been top-heavy. Never quite with the same strength in depth as the top top sides like Brazil, Spain and France. A bit like Portugal.
Let’s be fair, playing with Aguero, Tevez, Di Maria and co is better than with Postiga, Nuno Gomez, Simao or Dani (Nani even missed 2010). When Ronaldo had in team Figo and Deco in midfield, Messi was playing second fiddle to Riquelme. And later, he has Cambiasso, Veron, Banega and Di Maria there. In defense, they were pretty even.
I think if you check squad monetary values, Argentina was always higher (except in this World Cup), maybe twice as high.