Sony didn't force Raimi to have Peter Parker do a saturday night strut and make Sandman Uncle Ben's killer. I hate those far more than I hated Venom in the film. He could have worked Venom into something watchable but failed. Also I never heard anything that Sony didn't want Vulture.
SPIDEY 3's failure wasn't due because of any one
scene. Rather, it's quite obvious from the movie that Raimi wanted to give the Sandman and Harry stories emotional weight and was forced to put in the Venom storyline to a big degree that it could be used to sell the film, however, he had no affinity for Venom. So he had trouble taking his two plotlines he wanted to do and bending them tangentially around Venom. Hence why Parker does the strutting and ridiculous woman-beating dance, why an idea like Sandman being Ben's killer just couldn't hold up, and so on. It's not like, "Scene Y was bad, the film failed" but rather all the creative decisions that led up to the final film were shaped by Raimi having to accommodate a studio mandate he didn't care for. Sure, Venom absolutely could've worked in the movie, but he had no affinity for the character and spent his energies trying to salvage the characters he was interested in. Essentially, it's a case of "I had to murder my baby, or let someone else do it" as William Goldman said in his book WHICH LIE DID I TELL about one of his writing gigs. Raimi had to gut his third movie to make room for Venom and it's just not easy to do. I recently watched all three Spidey's back to back and while I think all of them are dull and slow, the third one really lacks any charm the first two had. And so, in so far as I know, this seems to be what happened.
As for the Vulture; I honestly can't remember which characters were rumoured to be ones Raimi wanted and ones Sony wanted. I think Black Cat was mentioned as was Kraven, but I can't remember. I just remember the whole rumour mill was spinning with "It's going to be Spidey 3 all over again", and it seemed to be a matter of Sony/Marvel not wanting to have to go through all that crap again, so they jettisoned all the guys in the first three and started again. Which seems believable since Fox is planning on doing that with their new X-MEN movies. And possibly this is true of the James Bond franchise which is not only considering dumping Daniel Craig, but rebooting it
again. And Marvel/Universal did it with HULK. There's a definite trend at the moment that if a franchise has a big failure (X-MEN 3, SPIDER-MAN 3, QUANTUM OF SOLACE, HULK, STAR TREK: NEMESIS) they just dump it all, wait a few years, and reboot the entire franchise with an all-new cast, writing team, and director.
I expect this to be the case for THE LAST AIRBENDER too.