All in all, the 'clout' around 109s is more due to the pilots than to the plane, just be thankful grizz wasn't flying p40Bs, or everyone would be claiming they are 'uber' too.
That's misleading because the K4 has climb and speed unmatched by anything unperked in the game. Some planes are good in that they have
something over every other plane, be it turn, or speed, or what have you. But the K4 has two things over every other plane, speed and acceleration at Main Arena altitudes. What makes the K4 such an easy choice is that it doesn't matter what everyone else is flying, the K4 is better than it in the same two ways, only the degree of better is different. So these pilots choose it for its perk farming ability (thanks to its oddly high base ENY), the ability to leave any situation that isn't in their favor, and the ability to prevent anyone else from running away when the situation is in their favor.
So no, their choice of the K4 is not an accident or coincidence. Its a calculated decision, and they wouldn't be as dominant in any other ride, because they couldn't choose to leave any fight when the odds turn in another ride.
Now that I got that off my chest, Steve used to always say that the Yak-9U was a P-51 killer. I know when I fly a Yak I look for P-51s in particular.