I think something most people don't consider is that war is still about logistics. Every single soldier needs food, water, basic consumables, ammo, and more. And each group of soldier will need comms, fuel, and so on. With even a relatively small group of soldiers you rapidly enter into the domain of tons of supplies needed every single day. And in general the majority of an army isn't out there fighting, but participating in supply and logistics. It's called the tooth-to-tail ratio. [1] In WW1 it 2.6:1 logistics:combat, in the Vietnam War (with its lengthy logistics pipeline) it was 12.9:1!

Operating, maintaining, and expanding these logistics pipelines is essentially what war is. Drones can play a major offensive (and defensive) role, but soldiers remain the most critical component in war, and probably will for the foreseeable future.

[1] - https://en.wikipedia.org/wiki/Tooth-to-tail_ratio