I really hope this post is sarcastic.
Yeah, all go call in planes with no tanks and only Ostheer infantry, this can only end well
Pz4 spam, Panthers.
Here you have only 2 OST players but I asure you that planes crashes killed more units than all axis players.
The only army in the game with flexibility is Soviets because of the commander system. You can drastically vary your play style based on what commander you chose.
Soviets are the least flexible army because of commanders, not most flexible.
Soviets commanders fill the gaps. You need them to stand against Axis.
On the other hand, OKW does not need any commander in fact.
In tiers you have everything you need, and commaders give you something extra. That's flexibility. You can make AI units and then Pak43.
If you choose wrong doctrine as Soviets you are doomed, so where is this flexibility?
Ostheer is flexible faction as well. You need mortar? pak? sniper? 222? No problem you will have access to all of them.
You need sniper? Zis? Maxim? M3? Stop right there, you can't have everything. SO where is this flexibility?
Same for USF. You must chose between AA, MG, mines and zooks, light tank and AT gun. There is no flexibility for allies.