The principle weakness of the Ukrainian forces is people power. The west can supply the ammunition, and yes, there's a shortage, but at the end day you can bring things in. The Russians have supply problems too, but they can manufacture it and they are bringing it in.
The people issue is a factor that the west is not going to supply because we, the west, are not going to go to war in Ukraine. That means the Ukrainian military and the Ukrainian people have to do the fighting. There are only so many Ukrainian men and women who are prepared to go and able to go compared to the Russians.
The question is, are there more Russians than there are Ukrainians who can actually go to war and do the fighting? Right now, the situation suggests that the Russians are able to sustain themselves. They have not yet fully mobilized. They've done limited mobilizations. They could do more. Putin is trying to avoid that right now. He's balancing, but he has the potential. Ukraine has no more potential to increase. It is doing everything it can.