Spiderman is a marvel property mate but DC have loads of great characters. Wonder Woman, Green Lantern (who is a brilliant character that is unfortunately tainted by the awful Reynolds movie). Green Arrow another with excellent potential. Martin Manhunter would be interesting as would a Flash film with a non-cringey actor playing Barry Allen. They've got John Constantine, Swamp Thing, Cyborg along with the Titans and many other characters like Hawkman and the Spectre. They could use the New God's that may be completely unknown to your average viewer but have great potential if done properly. The Booster Gold character would work better today then when he was first created as a film character.
They also have so many side characters associated with their main associated with their big three. I mean they could do a series of movies about individual "Bat-family" characters like Red Hood, Night-Wing, Batwoman, Batgirl, ect and it would probably sell way better then their current DCEU at this stage and have loads more potential.