If that was how warfare worked, China would have controlled Vietnam, United Korea and many other places right now.
They are on the attack, their logistics suck, and they are forced to equip most of their huge numbers of barely trained manpower with roughly Vietnam era equipment, poorly maintained at that.
It's also a reason why they keep trying to freeze the conflict again. A few months to a year of ceasefire would allow them to somewhat unfuck the logistical, training and organizational issues, which would in turn allow them at least a couple weeks of effective offensive on the unfreezing before the logistics and organization would start to fall apart again. Which is precisely why Ukraine is opposed to letting them catch a breath in this way.