This is a good point.
Looking through comics and scrolling through hundreds of images the element that's most common to Doom's costume is his simple, plain green tunic (as on the S-Hero figure, or the Sideshow maquette that inspired Hot Toys' backdrop).
Yet Hot Toys have made it much more elaborate with stitching, panels and layers:
Occasionally a more elaborate design pops up, but it appears to be from cartoons, video games, card games, fan art or cosplay.
One of the possible inspirations is from the Marvel Ultimate Alliance videogame, with its panels and split skirt design:
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A Hono release might've been the preferable option, and Hot Toys may actually do a Hono later with a simpler, more 'classic' appearance. 'Classic' in that he's worn the plain and simple tunic for most his appearances over the last 62 years.