Without Spiderman, that's not going to work well as a standalone movie. Agent Venom is the best option here
Group/government captured an alien symbiote, combine with a host to make the ultimate assassin/soldier, soldier goes on missions for them, discovers dark secrets, fights against the group that created him
Added bonus is that soldier loses control of symbiote, letting us get both the enhanced soldier in the first half and unstoppable monster massacring enemies in the second
No superheroes, no superheroics, just a secret agent/spy movie with alien powers and maybe an action/horror vibe