He hasn't been as decisive as Barca for Argentina. Argentina still needs him though.
If you're speaking about the WC then yeah, even if he scored v nigeria or assisted v france, he's been far away from being decisive.
But he's been our best player and the most decisive by a country mile all the time, every WCQ, every tournment since 2012.
Until 2012 he's been really far away from being our best player and being as good as he was in Barcelona, considering he was clearly the best player in the world, he won the UCL in Wembley in 2011 and then he had a terrible Copa America in our own country.
After Sabella took charge, and until 2018 WC, Messi has been decisive in every match Argentina has played.