If the MA were about anything resembling honorable or fair single combat, then one would have to be crazy to take up a D9, as opposed to a Spit, Hurri, or some other turner with sweet handling.
However, it ain't, it just ain't. Take up good old Spit, do a nice lead turn on the first bandit you see, settle on his six nicely, cut your throttle down to pull in real nice and close and give him the canns, and what can you expect? Generally, 2-3 of his closest friends coming in to pick or saddle up on you. (If the only other planes in sight are wearing green, you can usually expect them to all come in and "help" you with that con on your 12...but that's another issue)
If you think a Dora diving in at high speed to backstab you during a dogfight is annoying, consider the Hurri or Zeke that comes in and saddles up. (Not that there is anything wrong with clearing a countryman's six, I'm not the one complaining about "unfair" tactics.) Then consider that even the ones you kill will be reupping to come in higher and better-planed for vengeance...it's like fighting zombies in a graveyard. At this point, a plane with escapability starts to look real good.
Don't like picking? Many planes are much better pickers than the Dora, they have as good or better guns and can turn alot better. You want a real furball picking machine? Grab you a Nik. No, what the D9 is good for is assuring that if you don't do anything too stupid, you can usually leave the gang behind and land when its time to be leaving. The price it pays for this escapability is vastly inferior turning and that much more difficulty actually getting kills. A fair trade, IMO.
Not nesscarily a choice that stems from a timid personality either, perhaps an anti-social one instead. A fast plane makes it possible to fly and fight by yourself, without the guarantee of being ganged and shot down.
Whenever I hear a complaint about someone running in a Pony or a D9 or the like, I think to myself, does the person making the complaint REALLY wish the other guy was a vastly more competent stick, who would actually shoot down their (insert name of superior turning fighter here) instead of running from it? Or are they instead wishing that their less-skilled opponent would obligingly begin an unwinnable turn radius fight with them, thus giving them an easy kill? Clearly, it is the latter, and just as clearly, there is very little difference between this mindset and the mindset of shooting planes on the runway.
If alot of the D9 drivers are extending too soon in 1v1 situations where it might be possible for them to get a kill, that's their loss and no one else's IMO.