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In regards to Barbarossa being a TOTAL WAR and not a quick one. You have to remember the germans 'gambled' on the idea that they would be able to quickly destroy the RKKA west of the Dnepr and that this would lead to political turmoil within the USSR, people would revolt, the internal political leadership would fight amongst themselves, just like happened in 1917.
Then Germany could sweep up the remains and hey, GG. "Kick the door in and the entire rotten structure will collapse."
People often stare blindly at military matters and forget political ones. Kiev is my favourite one.
600 000 losses for the RKKA that could have been pulled out sounds like shit decision making.
Or abandon the 3rd city of the country and the historical cradle of your civilization without firing a shot? Good luck maintaining morale and trust in the government by regular people. Especially in that region of the country if you ever manage to get it back. "Hi, we kinda left you to fend for yourself for two years under occupation, hope you don't have any grudges against us, anyway we want you to listen to us again now"
Much better to try to fight and loose horribly in military terms, but using it to get people on your side; than it would be to retreat the army intact and loose the people.