I don't think opening against the Flash is necessarily a problem by itself. Pixar has shown it can go toe to toe against big films and still thrive. Inside Out, which Elemental shares some similarities with, opened in #2 but still debuted very strongly against Jurassic World's ~$107 million second weekend (which is probably on par or even higher than what the Flash would gross its opening weekend). But combined with everything this summer, I do agree Elemental could have an issue finding the right audience.