I believe the ten to one ratio of Artillery, even maybe 20-1, at a given time and place. Offense gets to pick the time and place to concentrate, defense has to be everywhere.
It seems that that phase of the war (Russians able to just consistently blast their way through with tube Artillery) may be over, with the new ability of the Ukrainians to disrupt Russian Artillery supply with deep strikes. We will see if Russian forces can counter, or adapt to, that new situation.
I have not heard much about the counter-battery battle, to know if that has shifted as well. The relatively sudden lessening of Russian Artillery fire might also have been precipitated by their Artillery batteries getting hit with newly effective counter battery fire, and them pulling in their horns while they analyze the new threat. That is just a possibility I am considering - I have not seen indications of that (although I have been anticipating some such capability would be forthcoming, as the Ukrainians were being so effectively pummeled by Russian Arty).
“The relatively sudden lessening of Russian Artillery fire”
I just heard that they opened back up on Bakhmut yesterday with heavy fires, so Russian Artillery barrages are still a thing, even if it is changing a bit.