I'm not the right fellow to comment on the accuracy of the D9's flight model. If you want to discuss that, I suggest a post in the Aircraft forum. You'll get more informed opinions there.
Now, about how to use the Dora's strengths... and yes, it can dogfight, it just can't turn! The Dora is a great E fighter, it is fast and accellerates well combined with good dive, zoom, high speed handling, and a great roll rate. In addition to it's E fighting qualities, the Dora can dictate the fight to most other planes in the game based on it's pure speed and great accelleration. To be successful you must start fights with an E advantage, and fly in a manner that protects that advantage. You must use vertical moves whenever possible, and rely on lag pursuit, lag displacement rolls, and any other moves that conserver your speed and energy while maintaining position on the bandit. More than anything... USE THE VERTICAL LUKE!
To be honest, the D9's turning ability is pretty much irrelevent. If you have to rely on that, you are screwed anyway. That's like relying on the Zeke's speed and toughness to get you out of trouble.

Simply put the D9 MUST have an energy advantage at the start of the fight to expect to win. It's like the Jug in this regard. On the positive side, this plane has the speed and accelleration to disengage almost any other plane until you can get that advantage. You can even use high speed shallow climbs to turn the E tables on your opponents if you manage your speed carefully and know the performance of your plane and the other fellow's.
Versus the La7 and George your problem is that those planes are pretty fast, and they can accellerate very well. This give you two problems in an E fighter like the D9. The first problem is that they can gain E very very quickly, which means that your energy advantage gets lost more quickly than it does versus other planes. The second problem is that these planes often dive well, especially in the early part of a dive, which can make it very difficult to escape from them. Actually there is also a third problem... both can hang on their prop pretty well and shoot up at you when you are using vertical moves. These are not unbeatable planes by any means... you just have to adjust to compensate for their strengths when fighting them. It means you need a greater E advantage to take them on, and you have less passes to do it in. You have to bug out sooner and with more speed than against most others in order to escape. You also have to have more vertical separation to be safely out of range of their guns if they decide to zoom to you and try for a shot. You don't want to try and rope-a-dope these guys, they are too good going up.
The dora has all the tools a good E fighter needs. Good speed, good accelleration, good roll, great initial turn rate, decent guns. When I say E fighter... I don't mean BnZ, I mean a real dogfight where you don't extend beyond D1.2 or so and mostly are much closer. Flown right, the D9 can dominate... even in a dogfight. It takes great skill to dogfight an E fighter, but that's why I love flying my Jug so much.

I think the D9 presents a similar challenge, and will provide you with similar rewards as you learn to master Dora's abilities.