It’s also air power. I think we’re all kind of ignoring that Russia IS gaining ground in the east. The long delay in getting Ukraine more ammo and matériel let Russia overrun entrenched positions.
I think the most positive way of looking at this is - you attack where you can and not where your enemy expects you to. Ukraine has never been able to reclaim territory in large amounts. So maybe in a peace deal they can “trade” territory instead.