>> Note that body exchanges were not this lopsided when Russia was retreating

That is the point. There are simply no Russian bodies in the territories controlled by Ukrainian army. To extract bodies they should be far from the front line, with current drone activity it's 20+ km. Body exchange says nothing about KIA.

If russian "meat" assault costs them a 100 killed to fulfill talk to capture a treeline - those 100 bodies will be on russian-controlled territory and not for exchange.