I dont think Russian losses have been catastrophic so far. Unlike Ukraine Russian leadership has used tactical withdrawals to preserve its military forces where they were at a disadvantage in battle and haven't forced them to pointlessly fight to the death to hold ground such as in Kiev region and Kharkiv oblast.
The partial mobilisation is a simple recognition of reality that if Ukraine is being supplied ongoing training, replacement of destroyed weapons and ammunition to conduct offensive operations then the small force being currently used in the Ukraine operation is just too small to properly defend all of the territory in the North and South and also conduct the ongoing offensives in Donbass.
Its a logical escalation made necessary by the NATO support of Ukraine pure and simple. How will NATO respond?
