First, I just want to clarify that if you like Zavok, that's fine, I'm not judging you. I just don't really like him that much.
Also, please don't say, "Remove him from the franchise. "
I'd improve Zavok to be more memorable by making him the opposite of Eggman. Instead of machines, he uses his bare fists and magic. Eggman wants to take over the world and build Eggman Land, Zavok just wants destruction. Zavok's intelligence lies in philosophy, where as Eggman's lies in science and technology. Also, instead of trying to just use the world's energy for himself, I think he could maybe try to just get rid of it all together, I dunno. And I'd change his appearance and get rid of the rest of the six,