Ukraine

It indeed is. According to minusrus site Russia had ~5700 artillery units when war started and I highly doubt that they can manufacture new ones faster than they're losing units, not to even mention ammunition shortage and logistics issues.

They're not completely depleted yet, and most likely never will be as new units are pushed out every day, but advances at Crimea (among others) suggests that their capabilities are dropping, so once mine fields and fortifications on the lines fall there might not be that much in the way before Ukraine reaches 1991 borders.

It's still going to take time and monumental amounts of effort, equipment and (unfortunately) Ukrainian lifes before Russia is forced out of their country, but I strongly believe that it will happen. The west, and Europe spesifically, just need to keep up with demands from the field. Letting Ukraine fall would be catastrophic for stability in whole Europe and even globally.