Topher Grace did what he could with what he was given, and he wasn’t necessarily bad, he just didn’t feel like Eddie Brock.
Personally, I found Topher Grace somewhat cheesy in the role, but given the tone of the rest of the film, I have to think that this was more a directorial choice than any sort of failure on the actor’s part.
Thomas Haden Church’s Sandman had a real emotional arc, but it was as if they studio felt he wasn’t flashy enough alone.
Frankly, that’s sort of how Venom felt in the film.