Charge, I agree that the points you mentioned have a recoil reducing effect. Still I think the difference is quite big. There are many sources discussing about IL-2 and Yak-9T which mention that the recoil of the NS37 was such that only couple of aimed shot could be made at a time because of the recoil. That is almost the case for the Hurri2D but not for the IL-2 with the NS37.
Btw, I played a bit more offline and got the IL-2 going 40mph backwards on the runway concrete and it was still firmly accelerating.

By calculating friction force caused by the runway (assuming the friction is linear) and using cannons to accelerate to a certain speed the acceleration and the force needed for it could be measured. Idealizing the recoil force as constant force and counting the rounds it takes to accelerate into that certain speed horisontal force component of a single shot could be isolated even though the RoFs are different. To measure the exact angle at which the planes are sitting on the ground might a bit tricky though. That would be needed to get the total force per shot.
...but I think I'm a bit too lazy to test this. HTC knows the numbers they are using and I'm hoping they are aware of this thread and check their numbers. If there is a discrepancy on the recoils between these weapons I hope they adjust the game accordingly.