If anything, Pure Evil Boo shouldn't be any different than Kid Boo since he represents all of the evil within Boo. If Mr. Boo is supposed to be a Boo free of evil, and Pure Evil Boo is a Boo full of evil, then where the hell is Kid Boo?
Basically, Fat Boo-Evil=Pure Evil Boo
Super Boo-Mr. Boo=Kid Boo
Some think Pure Evil Boo having a Kaioshin outfit means he's influenced by them, but that doesn't make sense, either. Mr. Boo is basically Dai Kaioshin, and South Kaioshin didn't have a positive effect on Boo's evil.
Removing the evil from himself manifested into another Boo altogether. Removing the remaining good from Super Boo reverted him to Kid Boo. They're created through different methods, but Pure Evil Boo, on paper, should be no different than Kid Boo.