Yep, that is my general feeling. "Able to generate a darkness field dispersable by regular light" is like an even rarer form of "can explain the escape with wish" or "can explain the earthquake with Earthquake SLA". Yes, ideal if it does come up, but so rare that most decent suggestions do without.
In the entire history of this thread, I believe it has come up once - a creature of the underdark of Forgotten Realms, IIRC, had a weak magical darkness that didn't work in daylight.
GW