"Says here, a group of superheroes want to defeat me, for no other purpose than to do it..." Of course they couldn't defeat Jon, anyone like Dr. Manhattan who can make any matter in the Universe simply vanish is simply unbeatable. He doesn't need nourishment of any kind, can pass through objects, can teleport himself possibly anywhere in the interstellar Universe, the range is unknown. He can reverse entropy, walk on the surface of the sun, has complete control over subatomic particles, (though I assume it would have little effect on The Forgotten One), his emotional capacities have lessened so Jean Grey might not have the effect on him one might expect from Male/Female interaction. Bottom line is he could simply replicate himself many times over, each with independent function and equal power, creating 8 or more of himself to take on the 4 superheroes. There really is no combination of four DC or Marvel that could match him, but IMO the best chance would be Thanos, Galactus, Thor and Hulk, even then probably not.