I understand the logic and it's flawed. This isn't about the mundane " Brock & Peter are mirror images of each other " ( yawn), it's about Raimi exploiting a beloved character for money without giving him his due. Since Venom's inception, Spidey has refered to him as his most dangerous foe. Thus, Raimi should have had the common sense to bring out this very important turing point in Spidey's life and not muck it up with any Ultimate Venom sythesis because he doesn't "get" Venom. How juvenile can he be?
Instead of the goofy looking "evil twin" character, we could have ( should have ) gotten a massive, terrifying, slobbering, rampaging beast that was nonetheless intelligent and resourceful. That is the only storyline befitting of an uber-villian like Venom. Raimi owed it to the character and every Spider-man fan who has ever enjoyed a Venom story.