The early ground vehicles and research-based necroplanes are in an awkward spot.
Ground vehicles are basically useless because the little bird exists, at the same time if the little bird and angry bird didn't exists having to use ground vehicles to start from scratch would really suck. You have literally nothing to arm them with other than your starting assault cannons because it will be months before you can make more cannons or get them from fort defences, and months further still before you will even SEE a grenade launcher or RPG in enemy hands, let alone be able to buy them on the open market. So your best hope is to load up the cannons and pray that you can loot a light machinegun or gecko from hoverpods so that you can start killing bandit cars and then get better guns for war trucks and so on. Even if you ignore the little bird it's so much easier to just buy an angry bird since you can research it very early.
Necroplanes have a similar problem in that the little bird exists and is adequate for every enemy you will actually find in the early part of the game, not to mention that the tech that enables you to make necroplanes also gives you the ability to buy new little birds, and the next tier up of enemy aircraft are all aircars that require aircar speeds in order to catch. So they're basically redundant despite being research and material intensive because they jump from superfluous to obsolete. You can get to them early if you focus your research there, but new players have no idea what the prerequisites are and I only unlocked them after aircars because better interceptors than the little bird were such a low priority.
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One thing that might change that calculus would be the addition of new hangar types. IIRC there was talk of having at least two sizes of hangar, since single ground vehicles like humvees are tiny compare to aircraft that would let you deploy more of them out of the same base and keep ground vehicles into the late game for special missions. Necroplanes should be able to fit into a smaller hangar because you are only performing maintenance there (they are not VTOLs and need a runway to take off).
Another thing would be more mission types with restricted equipment that makes sense in context. Some missions require ground vehicles or undetectable vehicles like the big bird for a "stealth" approach. Ground race missions require ground vehicles and so on. There should be more of these in the early game when your air capacity is much weaker, and later on they can taper off and be replaced by new stuff (which is how most mission types already work).