aguero and higuain are goalscorers they don't create they finish. as for lesser teams croatia has arguably one of the best midfields in the world. 1 from barca, 2 from madrid, and 2 from inter etc. nigeria has very strong, physical and really good defensively minded players, mikel, ndidi, moses, etc. you need real quality in midfield to beat them comfortably. iceland well i take it you watched the euros? enough said. they are a good squad, little individual talent but a really good team who plays as a unit.
di maria is a winger he's also completely 1 footed. all you need to do is show him onto his right foot and he fails. he is easy to subdue so long as you can match his pace. so you don't know much about him tbh. he isn't that good when you know how to play against him. take away his goals for PSG as we all know the french league is crap. he scored 25 goals in 5 years playing for 2 of the biggest teams in the world. in 30 appearances in ligue 1 (a crap league) he has made 6 assists. 1 assist every 5 games. he has scored a lot there more than he has before and that is in particular due to him being very greedy, likes to overdo things when a simple pass is on he would rather take another player on as he maybe beat 1 or 2. this works in ligue 1 and that is why he is scoring. psg are leagues ahead of the pack.
so no he isn't good enough to destroy teams like nigeria, croatia or iceland by creating chances. so they are relying on the likes of banega and biglia and let's face it they aren't exactly world class playmakers.
they need a manager who can play to their strengths. they have 4 world class forwards. aguero, higuain, messi and dyabala. but with no real playmakers. it's far from just ,messi and only messi. their team is great lacking creative midfielders therefore they need to use tactics to compensate. something their manager seems incapable of.
Aguero and Higuain have chipped in with a few assists for their clubs and are players that win games with something from nothing. They have been doing neither for Argentina and there's more to that than who is playing behind them.
The issue is not just for these championships, this has been going on for a long time. It seems as though Messi manages the team a lot of the time and it is clear that whenever an Argentinian player gets the ball in the opposition half they look around for Messi, even to the point where sometimes they lose the ball as they lose track of what is going on about them. Either that or they play stupid balls to him rather than take the better options. None of that has anything to do with Di Maria or whoever.
The manager though is terrible for the fact he seems completely overwhelmed by the job if nothing else.