It’s true that SBRs are nearly a break-even proposition. However, if they weren’t, they’d dominate the game.
The whole point of SBRs is inflicting damage that the enemy can’t afford. The US is the only country that can really afford an SBR campaign, simply because it can afford the losses, while Germany can’t. The US sacrifices its own income to suppress Germany’s so that the UK and USSR can take advantage of its weakened state. This is not really pointless.
If SBRs were a money-making proposition, there’s no way that the Axis could survive, since they start off economically inferior to the Allies. The Allies could simply build a few bombers to SBR with, then devote the rest of their income to defense. Eventually, the combined toll of the bombings would render the Axis powers bankrupt, then the Allies could move in for the kill. Doesn’t sound like a very fun game, does it?
The strategy you’re describing sounds perfectly viable to me.