At the moment artillery is an all or nothing weapon
Actually, it is.
Many years ago, when military service was still compulsory in France, I spent one year in the Artillery and I did some training as an artillery observer. You are on the top of a hill with a radio (of course in WWI it would have been a wire telephone) and you look at the landscape and when the instructor shows where the target is supposed to be, you look at the map and you tell the target position in the radio and the battery officer orders fire following what you said.
If you did it wrong, the shells fell somewhere very far from the target. If you did it right, most of the time the two first shells do not fall right on the target, they fall 100 or 200 m from it (because of wind and other factors etc) and you have to correct your orders and ask for more.