But the odds of success per round are:
No Bombers shot down: 33.14%
1 Bomber shot down (or less): 74.42%
That means, almost 75% of the time, you will do more damage to Russia than you will sustain to either Germany or Japan. Mathematically/statistically speaking, the theory is sound. At 15 IPC per bomber and only a 25.58% chance of losing more than one bomber, you are looking at a loss of 11 IPC on average to the axis.
Meanwhile, you are looking at a mean result of 3.5 IPC in damage done per bomber. 6 Bombers * 3.5 IPC in damage is 21 IPC.
So you, theoretically, do 21 IPC in damage to Russia each round and take 11 IPC in damage each round (and that 11 IPC is split evenly between Japan/Germany, so figure 5.5 IPC to each Axis but a full 21 to Russia.)
Now, I am not going to sit here and tell you that statistics is 100% accurate all the time. Sure, I’ve experienced the event when 3 bombers attacked an AA Gun and 3 bombers were shot down by the AA Gun. But assuming a normal distribution of results, rolled on a fair die, the potential damage to Russia far outweighs the potential risk to the axis - on paper.