Agree, D9 was anything but a buff interceptor. Is is a more than capable fighter, IMO, far superior to the P51 (except in range). The MAIN problems with D9 in AH, imo, are two:
1 - Absolutelly horrible guns performance and aiming, the very worst weaponset with a huge margin (except C202).
2 - Ping = engine out or ping = radiator out. No radiator = 15 secs flying.
In the other hand, acceleration is good, substained climb is good, zoom climb is average (even with lo drag!), roll is good and dive is good.