“Destroy the artillery piece and you have no way to shoot those 300 million shells.”
Actually it’s likely more than one ‘piece’, so yeah, destroy 1000 of them, and they’ll just send over another 2000.
Not so easy...
Maybe the Russian guns will wear out after a while? So much use will cause the barrels to warm as they overheat? In time the whole of The Dombass will look like a Verdun Moonscape so when Russia get it—it will be worthless.