SupremacyKing2
Deity
There are no 'stacks'. From the sound of it units Like AA and anti tank can be embedded into modern units so they act more like promotions allowing players to customize their units to defend against specific threats.
The corps and army system allows the creation of stronger units but combining 2 similar units ; Doing so doesn't double the power of the final unit. It only increases by 40% but it will still be a single unit on the map, not a stack of 2 units.
I get that it will be a single unit not 2. But the difference will be that instead of having a separate melee unit and a separate support unit that you have around separately (civ5 1upt) you will have a single unit that is the function equivalent of the two. So, it will work as if you had a stack even though you only have 1 unit.