Here is the official trailer of Venom from Sony. How a Venom movie is suppose to work without Spider-man is going to be interesting. I think this movie will struggle because of the fans being uneasy about a Spider-man-less Venom movie.
A Venom movie without Spider-man could have worked.
The only way I could have seen this work if they would have done Agent Venom. They could have set the movie in space and capitalized on the space opera of Star Wars and Guardians of the Galaxy. This would have made it easier to make a movie without Spider-man as they could had referenced him in the opening. And since the movie would have been in space they could have played with the idea that they were in the future on a distant planet learning more about the Symbiote world.
A new world and a new story
Though the symbiote planet was a Gaurdians of the Galaxy (GoG) story, they could have easily adapted it into what Sony was trying to do. And since majority of the public would not have known or cared about it being an GoG story they would have the liberty to play around with the concept without all the backlash.
Sony backed themselves in a corner already botching Venom once. The iconic villain needed the right touch and story that was not crammed into another. It needed its own story that focused on the struggle between the character and the symbiote battling for control. Two separate characters having to co-exist to accomplish a goal. Needing each other in order to survive. A failed story opportunity by Sony.