Personally I think it's less of an issue for a TV show than for an RPG session. All the characters in The Wire or Cheers had about the same powerset. Personalities and complications are what drive the story.
If you really need to define the characters in the action sequences, you could have Luke be more of a brawler while Jessica shows more real-world technique like muay thai and krav maga. Danny would use more cinematic kung fu moves, setting up opponents for finishing with the Fist, and Matt would use truly ridiculous acrobatics.