Wilbur doesn't do arbitrary reprojections to equirectangular, that's more what ReprojectImage does. That looks pretty much like a Miller Cylindrical projection. ReprojectImage didn't do well with it, most likely because Reprojectimage was never intended as a high-accuracy tool (it's as good as you're willing to clumsily adjust things).

Anyhow, here's what fell out (it's upside down, but I think that you can fix that):
Click image for larger version. 

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