It seems like the "Co-Prosperity Cloud" is a joke, but even if it is, it's a joke in poor taste considering the atrocities committed by Japan, and not even an especially clever one (annexation and abuse for profit is not really the same idea - I hope - that Pinboard is expressing).
In "jokes", people often state propositions that seem opposed to what we would hope they believe.
In any case, the above fails the first rule of jokes... they're supposed to be funny. I thought the post was funny enough. But the reference to a co-prosperity system didn't add much (any?) humor to it. Just pointing that out to the OP...
Repurposing the stilted propaganda of long-ago times, or of clumsy tyrants, for subtly absurdist/ironic humor value, does not in any way lessen the original horrors. It celebrates the distance we've achieved, while also offering a teaching moment by contrast/reference.
See also: "we will bury you", "let a thousand flowers bloom", "we had to destroy the village in order to save it", "i have in my hands a list of hundreds of known Communists", "the war to end all wars", "the mother of all battles", "this blogger has been harmonized", etc.
Personally I thought the co-prosperity added to the humour with an over-the-top name, and I detected a slight whiff of Eastern Bloc over-the-top naming, akin to Council for Mutual Economic Assistance or Polish–Soviet Friendship Society. But then my ethnic background is Polish and not an East/Southeast Asian one.