I've played around with the idea of this as a toggle, depending on setting. In a supers game (as you suggest), there would probably be only one character (or a minority of group members) taking Criminology or Forensic Medicine and there's really no need to break it down further. If we are playing Police Procedural Hero, all the characters will have it, so we need to flip the toggle. Now, using the main skill requires subskills (Knowledge Skills related to the main skill) to use it effectively. Using the main skill without at least a Familiarity in the relevant subskill would have a -3 penalty because they don't have the more specialized knowledge needed to effectively apply the main skill. Higher levels in the subskill would allow a complementary roll, as usual.
Example: Detectives Willams and Hunter analyzing data from a crime scene trying determine which direction a gunshot came from. Both have Criminology, but only Hunter has Ballistic Analysis. Detective Williams will take a -3 to his Criminology roll.