I wouldn’t call Raimi a sellout. If he had his way, he would’ve made a nice little trilogy, but the studio got too involved and ruined the franchise. Burton didn’t sell out by doing the Batman films, he could have if you watch the interviews on the DVD’s he was offered part three but with less control, which means the studio wanted to take over. This is exactly what happened with Raimi. The only way to do a proper trilogy without studio interference is to go ahead a make two at once via Matrix, LOTR, and Pirates.
The fact remains that Raimi did not want to do Venom, he likes the traditional villians. The studio then took over and asked everyone at the Comic Con who they wanted, and well that was it. Raimi simply lost control of the project because of the success. The problem lies with the fact that Raimi and Burton before him, just were not powerful enough to do what they wanted. By power they need to have proven box office success on name recognition only. Few people can do this in Hollywood, Speilberg, Tarantino, Lucas, Hitchcock before them. That kinda power is rare in Hollywood, but once the studio feels they made the director who he is, like Burton and Raimi, they feel they can do what they want because they grandfathered the project and the director, so the director has no real say so.
I hate to say it, but I believe this was going to be the situation with Bryan Singer’s X-Men 3 anyway. It would’ve been a bad movie no matter what because as far as I hear they didn’t want to do what he wanted to do, and not only that Superman was looking better than the studio’s version of X-3 which turned out exactly what Singer feared too many mutants and no tying up of the story he wanted to tell.