This is also a very excellent analysis. IMO, pay particular attention to Richard Shimooka, an analyst with a Canadian research group, starting about 12:19, discussing the hollowness of the Russian defense industry due to its cost in a rather small economy and the huge corruption of the Putin regime -

Reasons for Failure? Russian Air Force in Ukraine

https://www.youtube.com/watch?v=_WGcfkqzUI4