You can also style the SBR as a contrast to attacking the same TUV in regular battle. There are many times when UK planes (or another power) end up attacking by themselves in order to kill a few crucial but cheap land units or soften up a crucial weak point with a 1-2 punch. If I lost 1-2 bombers killing 1-3 blocking infantry, I’d regard it as a good tactical trade even if I lost 24 to 9 TUV.
There is no ## to ## comparison here–if the UK planes open the way to victory, then a sacrifice even of the entire airforce is “worth it” no matter what the numerical or economic trade offs are.
When you bomb out a power, (especially USSR with its limited $$ and scope of units), you are “killing” units before they ever exist, which leaves your opponent weaker on the counter attack and he is not refilling Moscow each turn instead he is paying off damage. This leads to a lack of crucial counterattack units against the japanese backdoor at a critical time. Russia is weakening itself with every re-take that it has to make, and the fact that units are being lost that would have been placed in the crucial backfield at the crucial time (R3-6) is a devastating combo.
When you add these things to the fact that Germany is producing 2:1 IPCs than Russia, it should make clear that even if Germany loses more $$ value of bombers, or that it seems like a lopsided $:$ trade (it is) …that is a very Germany+ trade for most of the game, and especially against Russia.
The dynamic against Germany is reversed; Germany has 26 production capacity and can even capture more. It has a $$ advantage early on, and has a 2:1 $ advantage against UK or USSR alone (and it has x2 as many bombers as the allies most of the time). Most importantly, the number of choices and targets mean that Germany should be able to produce pretty much unabated no matter how many bombers come or how many it shoots down. It also has many more fighters to stop those bombers. That means that bombers lost bombing Germany are lost at an overall disadvantage that is the opposite of the Germany-Russia+ trade.
There is an allied bomber breakpoint where this is no longer true (its about 7-8 bombers+) where the allies can saturate every SB target but typically they will then use the bomber stream to kill units not hit factories because once you get enough bombers, they can destroy a fair sized stack without much help…
the only way to alter these dynamics is to pile on those fighters. You already need them for defense, and unless German fighters can come (less likely than bombers being able to reach) once you have 3-4 fighters on a factory, they have to really think about coming in alone. London and Moscow and Tokyo can reach ## of fighters that can dissuade SBR without much alteration in how they typically buy.