That's interesting but not surprising and it doesn't affect the fact that the movie itself became Chaplin's most popular film and spurned widespread denouncement of the Nazi regime in Hollywood and consequently the rest of the USA until we entered the war in 1941.

As for Chaplin himself: as I said it's not surprising that he himself would lose popularity in spite of the success of his film. The popularity of artists and entertainers ALWAYS goes down when they make politics and personal opinion a defining characteristic of their career and public image. Case in point for the game industry is Phil Fish. No matter what people think of that guy, most people agree that FEZ is a good if not a great game. Same with Chaplin: great comedian, but divided opinion about his political views. For the time, anyway.

The bottom line is: people across the political spectrum are often tied together by the creative works of individuals like these but schisms can just as easily be formed over the creators' viewpoints, and the two things shouldn't be confused because they're separate and highly independent of one another.

EDIT: I think I should clarify a slight inaccuracy in my last post though, anti-Nazi sentiment may not have been particularly strong in the USA when 'The Great Dictator' came out, but the film DID kickstart anti-nazi sentiment across the US, such that by the time Germany declared war on us, the majority of the public weren't exactly on friendly terms with them anyway.

EDIT 2: I should also mention that that same article you quoted lists many other reasons that Chaplin's popularity declined sharply through the '40s and '50s. The views he expressed through 'The Great Dictator' were only a part of it. And he lost popularity through 'The Great Dictator' not because it blasted Hitler and Nazism, but because that ending speech you linked was perceived by the public as anti-capitalist (which was a whole other issue entirely). Bottom line is, people weren't really offended by the film's lampooning of the axis powers. And if you read elsewhere you will see that the film did have a significant impact on the public perception of Germany in the US.