Just 3 a month? That’s it? That’s nothing for the population of former Soviet Union back in the ‘80s which numbered over 300 million.
Afghanistan was to Vietnam was Vietnam was to WWII. Relative to Afghanistan, the amount of fighting was an order of magnitude higher in Vietnam. The fact that the Soviets could only deploy 100K men in Afghanistan vs our 500K in Vietnam says that the Soviet economy was staggering like a punch-drunk boxer. Whether this was the weight of subsidizing basket case client states like Cuba, South Yemen and Angola or the accumulated rot of 60 years of Bolshevik rule, the Soviet economy was not up to task of supporting even a small scale war like Afghanistan. My guess is that if they had launched a conventional war against the West, Soviet units would have been annihilated.
The part that’s truly incredible is that the San Diego is 8000 miles away from Saigon, whereas Afghanistan is right across the border from what was the Soviet Union. And yet we were able to put 500K men in Vietnam and feed them ice cream and turkey, whereas the Soviets had difficulty providing their Afghan-deployed force basic medical care. Disease rates for Afghan-deployed Red Army units soared to the extent that the units actually available for combat were a fraction of the deployed force.