yeah but only for the master, that's like one stun out of the bunch as compared to like giants who can stun a whole group
I haven't actually used razorwings very much in D2E, but their high move is not something to shake a stick at.. From my memories of D1E, they can swoop in, attack, and then fly back out of range very easily. The ability to ignore obstacles and other figures (due to Fly) also makes it really easy to get away again.
The fact that the master has Stun is just adding insult to injury (pun intended.)