In the Great War, a French officer said, "artillery conquers, infantry occupies."
I think that still applies, especially in the Russian context. The Russians bombard the crap out of a place, and the infantry occupies the rubble.
Rooting those Russians out of a piece of terrain once occupied, however, is another matter. It does not take a lot of Russian artillery for the Russians to retain a piece of land (although, obviously, it helps).
Thus, the fact that the Russians are momentarily low on arty ammunition (and arty ammunition throughput) does not make the Ukrainian task that much easier. The Russians still have to be pried out of their trenches which, since about 1914, has been a tough proposition.