S.D.Z could not be shot down yes, but on the other hand one A.S.D could not be stolen and did not need a sector to be used.
S.D.Z did not give you more resources it bought you the resources in normal price 200MP=150MU=50F
A.S.D. converts MU to Fuel and as all manipulation had a premium.
If you actually read my analysis for the difference in flight paths, number of planes and time to react you will say why the abilities are not fair to be countered either on the air or on the ground.
no one gives a fuck whether it can be stolen or not when it doesn't arrive.
resource conversion values are not 4:3:1, they're 5:2.5(or 3):1. source: someone at relic over a year ago.
the allied supply drop had a very serious issue with OKW, particularly right after WFA release, because the base defense took a lot of shots at it and the T3 flakHQ is also very good at shooting down planes. i've never seen the luftwaffe plane get shot down before giving the fuel. there's also the issue that on a lot of maps you effectively cannot steal the fuel/munitions because those points are safe. then there are maps where you effectively cannot use those abilities because the fighting happens right on top of those points. that's more of a map design issue than anything else though.