Why not have it spawn the fuel where it crashes? Then it can be potentially stolen, like the luftwaffle supply drop zone. At least then the ability remains useful in a risk/reward way throughout the game.
I like this idea.
OKW base defense and T4 shouldnt shoot down planes, only counters that you actually bought to counter should, like ostwind/M5/AAHT etc.
They should also remove the tendency of units to bunch up very tightly in cover, especially craters. Especially with smaller squads the oneshot wipe potential is huge due to a random unlucky mortar shell etc.
Although that could pose a problem where craters couldn't be used as cover, if the entire squad doesn't fit there.
Could you post a replay so we can analyze your gameplay.
You can counter Mortar pits and other emplacements by building a IsGs as OKW and barrage it, dont forget to reposistion your IsG when the mortarpit/bofors tries to barrage your IsG.
You can also force a brace (with IsG) and attack it as brace is almost over so it dies to a couple of pak/shreck shots or trow a incendiary nade.