Superman may have his name on the marquee and Brainiac may be bringing the big threat, but Man of Tomorrow could belong to Lex Luthor.Nathan Fillion, who returns as Guy Gardner in James Gunn’s upcoming DC Universe sequel, has offered an interesting tease about the movie, revealing that it will spend more time digging into Nicholas Hoult’s Lex Luthor and showing audiences who he really is.Fillion was asked whether Man of Tomorrow would have a sim…