this could happen easier than a lot of people suspect: Doom has displayed mental powers more than capable of breaking through Hal Jordan's defenses. Superman's weakness and power source are essentially the same thing: types of radiation. Doom has more than a few alternate types of energy projections and draining mechanisms that affect radiation and light spectra. Doom has experience with speedsters in the form of the Avenger's Quicksilver. Between a combination of anti-gravity, inertia dampeners and friction negation Flash is a sitting duck. As for Wonder Woman, he might be able to just out-muscle her but given her mythological origin it wouldn't surprise me if he had mystic means to depower her. Batman's got his work cut out for him; fighting against a man who has stood against Galactus, Strange and Satan, finding the weakness in a suit of armor Tony Stark doesn't begin to understand, controlled by an intellect that rivals multiple worlds' super geniuses.
You do realize the three people Doom fought in what this guy said could beat the main members of JLA? Also, he was able to steal the powers of the Beyonder ( a near omipotent being that can kill Superman easily). Wouldn't be surprised if he created devices to shut each of them down before he went there.