Almost all maps have some kind of safe fuel (+sometimes even ammo) point for each side. If you control no fuel point, the game is pretty much done for you, even the Allied Fuel Drop couldn't help you there. So the arguments of "you need control over a fuel point!" and "but the enemy can steal it!" are quite weak, if not even invalid.
The conversion rate is another ridiculous thing. You pay 100mun for 30 (mostly) fuel as ally. Meanwhile, Luftwaffe supply gets 50 fuel or 150 ammo for 200mp(you can even get fuel OR ammo). Manpower income is also about 4-6x higher than ammo income.
So, while axis are happily converting 200mp into 50 fuel or 150ammo, the allies have to pay 100mun for 30 fuel with a high risk for AA guns rendering the 100 ammo wasted and the doctrin as partly countered.
Apart from obvious reason that allied one is too easy to be shot down I still struggle to see why you think axis one is so much better. Having to pay manpower is obvious downside, it makes your field presence weaker and that is usually disastrous to map control and thus resources, making usage of ability questionably in many situations. In long run it may even work against you if is not executed well.
It is also not true that you always have fuel point. It is crucial to have same or more points than opponent, not to have a hold on one while opponent has the other, these points usually switch sides many times during match, in many situations they are in the middle of frontline what means that fuel ballance exist but the place is not safe enough to drop resources. It may even happen that all fuel points are either neutral or during capture through most of the game.
On the other hand soviet one is much cheaper - 100 muni on a faction that spends most ammo in mines and demos means 3 less mines for 30 more fuel, selling a mine for almost 10 fuel is a great bargain and it doesnt affect your field presence in any way. Only problem is that you can use the ability only if there is no AA on the field so it needs to be used at the very beginning of a game. Later on it can be even reliably destroyed by pintle mg so nobody would use it that far into the game. And here is the only problem. It should be changed so that only dedicated AA could shoot it down to make the ability more usefull.
There is also a need for bigger picture: the commander itself is very strong right now. Shermans would need some nerfs if allied drop was fixed the way I propose.