They are quite alike in engine-related performance, as per the official AH performance charts.
Whether or not the D9 can beat an La-7 on the deck 1v1 has no bearing on whether the D9 is one of the top fighters on the deck, and it in arguably is.
Now I will thank you to leave your hubris and compulsive need to be right out of the discussion.
Engine power alone is irrelevant. The Typhoon generates similar amounts of power on the deck, yet you aren't mentioning it as overpowered or worthy of being perked.
The LA-7, when caught low, can either extend away or go to a turnfight. The planes that are faster than the LA-7 cannot turn as well as it can (or cannot turn as well and use the vertical at the same time). Conversely, the planes that can turn better than the LA-7 are slower than it is. This allows the LA-7 to dominate any 1v1 fight at low altitude, as it can switch to the tactics type that its opponent is weakest in, while at the same time allowing it the ability to exit most fights on demand.
Not so for the D9.
The D9 can be outturned by all but 3 fighters in AH. Coupled with the fact that it can also be outclimbed by the K4 and the G-14; and acknowledging that it can be outran on the deck by the Tempest, K4, P-51D (with a light fuel load), and of course the LA-7, it's only viable attribute is its top speed. There is nothing "dominating" about the D9. If the D9 is not faster than its opponent, or if it is caught by a more maneuverable opponent, it will lose the fight given pilots of equal skill.
You're claiming the D9 is "just like" the LA-7 because of top speed, when in reality the top speed is the only reason why the D9 is even viable. Top speed is not the singular reason why the LA-7 is as good as it is. It has a great guns package with amazing ballistics and optimum concentration, it turns very well, and can transition from a turn fight to a knife-fight and then to an E fight with ease. The D9 cannot. The LA-7 is a dominant plane without its top speed; it's top speed is simply what makes it nigh unstoppable on the deck in the right hands. The D9, on the other hand, is nothing without its speed.
Similarly, the number of kills each aircraft get have nothing to do with the discussion. You can get 100+ kill streaks in a P-40 given enough time (it's reportedly been done). The entire issue here revolves around the survivability of each aircraft, on the deck, in an evenly matched, similar situation. The LA-7 wins by a huge margin in not only defensive flying, but offensive as well. The D9, unless attacking much slower aircraft, is primarily defensive when not in a group. It doesn't matter how the aircraft perform in groups, as we're discussing the individual merits of each aircraft and whether or not those merits warrant the aircraft to be perked.
I have no "need" or "compulsion" to be right; the D9 is the main aircraft I fly (I have over 5,000 kills in it over the last 12 months), and the LA-7 is the second most-frequent aircraft I fly (over 3,400 kills in it). I'm very familiar with both, and there is no comparison of the two on the deck, unless you think that top speed alone is what makes an aircraft great (it does not). I speak from experience.
If you can provide actual performance data in-game to the opposite, then please do. However, thus far, your entire argument has been "they both have similar top speeds and so they're similar aircraft," which lacks validity based on actual in-game performance.