If Amir was underrated or criticised, he only has himself to blame. There is no excuse for his pathetic performances for 2 years and he was one of the major reasons why we are ranked 6th today. Also, he has had zero impact in this World Cup for all his wickets, and that is mainly because he was wicket-less in his first spell against India and Australia. There is no use of picking cheap 5-fers and 3-fers when the opposition has a match-winning total on the board already.
People can blame the other bowlers as much as they want, but Amir has had a problem with taking wickets with the new ball for years now. Also, when other bowlers were taking wickets and Amir wasn't, he was still credited because he was helping other bowlers take wickets by "creating pressure". So what has happened now? Has he stopped creating pressure?
His fans will go to any lengths to make him the bowler that he is not. The only thing that has changed so far is that he is taking some lucky wickets in this World Cup. At least 50% of his wickets in this World Cup so far have been on nothing deliveries, and the Kohli one was a complete fluke.