One of the biggest differences between Marvel and DC's approach to television has been that of how the properties are linked. Marvel has opted to include all its film and TV properties as part of the same cinematic universe, whereas DC is not only keeping its film and TV worlds separate but allowing the TV properties to go off into either their individual or combined universes. The biggest difference is this allows multiple versions of the same DC character to appear at any one time - from both Grant Gustin and Ezra Miller playing the small and big screen versions of The Flash respectively, to a show like "Gotham" having essentially free reign to develop whatever villains they want.