NATO and US weapons and especially artillery ammo supply to Ukraine has dropped significantly, which was their main contribution. Ukraine is losing control of villages and land faster now. Ukraine can’t defend the 600-mile front, they are stretched too thin and being outfired 3 to 1 by artillery.
It’s a problem when you don’t have a widespread horizontal supply ability across a wide front line. That coupled with a shortage of artillery shells etc. could be a real problem in response. Russians have the depth of supply (even with older munitions) that can be ping-ponged in widely separated areas, IMO. That’s a problem to defend against