There are also new support class units, many of which were formally designated as military units in Civ V. These are units that are more sensibly depicted as special equipment embedded with a larger unit rather than standalone figures on the map. I’d expect the likes of anti-air and anti-tank units to fall into that category, along with other specialists.
It’ll also be possible, under certain circumstances, to stack two or three units of the same type to create a powerful combined force. These are exceptions to the non-stacking rule rather than symptomatic of a shift away from it.