>The planned economic system of USSR means that wartime production is a net economic loss serving no financial purpose.

It's a net loss under capitalist systems, too. Both systems can and do commit huge amounts of resources to pointless, destructive forever-wars. The political/military/security bureacracy of the USSR watched out for its own interests and sought ways to justify its own existence just as the military-industrial complex does in the USA.

The Soviet invasion enriched fewer bureacrats, but it also (compared to the NATO invasion) killed 10x more civilians and 3x more invaders in half the time, so in that sense I suppose we can say it was more efficient.