A good artillery team should be able to fire and scoot before counter-battery fire. And that's supersonic. You won't be able to do counter-battery with current drones. And an hypothetical supersonic drone is not going to be cost effective.

Drones are likely still great to opportunistically picking up artillery that is scouted by other surveillance drones, but it is probably not the best solution for attacking a battery that is currently firing, unless a drone happens to be already in position.