2.5 might be excessive but I was surprised to find that an autogyro rotor can have a “parachutal drag coefficient” of 2.0, see table 2 at page 8 here https://www.icas.org/icas_archive/ICAS2012/PAPERS/434.PDF
What is also interesting in the paper is the rotors alone have quite a decent L/D ratio (11 or above) which makes one wonder how a minimal (weight & drag) body gyro kite would fly.
It shouldn’t need to turn in a circle like a power kite dancing in horizontal eights or circles - it should be able to swipe left-and-right horizontally at a fixed altitude.
Gyroplanes and kites seem lots of fun.