SL reward is awful, I agree.
In Sim, it’s utterly unsustainable without premium aircraft - with 109F4, I can earn 730 SL/min maximum. Reality is 0.92 of that due to (Community Bug Reporting System).
At max reward potential - 15 x 0.92 x 730 = 10 074 SL earned per 15 minutes.
With my premium Mustang Mk Ia, I get
15 x 0.92 x 1015 x 2 = 28 014 per 15 minutes.
With the Ho-229 Horten, I get
1430 x 0.92 x 15 = 19734.
Now, what’s the Horten’s SPAWN cost? Not repair - spawn. You ALWAYS start with -17369. SL:

Let me repeat:
You start with -17369 and can earn at most 19734. Thus sums to 2365 SL gained for 15 minutes of gameplay. IN AIR SIMULATOR BATTLES. You know. The game mode with limited visibility and full-realistic controls (other than engine automation)?
2365 SL for 15 minutes of gameplay where you killed 2 people and got home safe and landed.
God forbid you didn’t land.
If you didn’t land, it goes to
19734 x 0.8 + -17369 = -1581.8
You read that right. 2 kills, survive for a full 15 minutes and die in the 16th minute and you’ve LOST 1581 silver lions.
So you respawn, and now you’re in a debt of -1581.8 + -17369 = -18950.8
Do you see an issue?
Do you see why nobody ever plays air simulator battles between 7.0 and 9.0 except for zombers and people using meta planes like saggitario 2 (8.0) and ariete (9.0)?