Goddamnit yes. Iron Fist has a detailed and mystical origin story all by himself. Luke Cage, as the FIRST African American superhero to headline his own comic series is black excellence personified and Jessica Jones also has a very detailed backstory as a hero/investigator. All 4 rightfully deserve their own 13 episode series.
Only thing that strikes me as odd is that they'd go with The Defenders moniker instead of Heroes For Hire. The Defenders is Dr. Strange, Namor, and Silver Surfer. Heroes For Hire is tailer MADE for this particular group given the relative popularity of the Luke Cage/Iron Fist team up, plus Jessica and Cage eventually marrying, and Mat Murdock being a lawyer.