I looked at the "drones", and it was a really cheap radio controlled airplane, another is a commercial quadcopter.
Yes, if you give them autonomy then poof! They're drones. That's how it works! I have a really cheap radio airplane-cum-drone right here, it's based on an old school Apprentice, before they included a RX with an integrated flight controller. So I integrated a mini Arduino Mega 2560, and a 9DOF board (I forget which one), and a BMP280 which at the time had the sweet spot for price/performance, now I would use a MS6511 or whatever it is.
And dropping the equivalent of a hand grenade. Like World War One biplanes tossing bomblets over the side by hand.
No! It's the opposite of that! You need to be either within sight or spend a few more bucks on a FPV rig (and the transmitters and cameras have both gotten quite cheap for moderate range now) and you can put it exactly where you want it.
Mortars haven't suddenly become useless or anything. That's not the argument. A drone is simply capable of being a new kind of bomb, in addition to the other things that it can be. With clever communications (cellular?) it can put your explosive exactly where you want it, without exposing the person who's placing it.