Earlier quoted context omitted.
Artillery with spotters accomplished the same task.
Except you can't survey an area with a an artillery warhead. Sure, you can use your spotters to scout ahead, but why put them in danger of an ambush and have them get killed by a sniper or hidden machinegun, when you can survey that area from a safe distance, and take out the sniper/machine gun if you see one? This is not meant to replace artillery battalions and scouts, but to complement them.
Kamikaze drones have a role for the smaller units, but at the battalion level, it's better to use a surveillance drone to coordinate fires from mortars, MLRS and artillery. The rounds fired from these systems typically have longer range than a drone, a higher rate of fire, and larger warheads.