It's not just corruption when most people engage in it to some extent. You would literally see factory workers bring stuff from their work without hiding it en masse and nobody would get fired. And then you would trade or share stuff you stole with your friends who stole from their jobs. Try stealing stuff from your own job openly every day, see how well that goes.
Now you have the burden of providing numeric evidence
Yes, because there is an easy way to measure how much everything costs in a system where monetary value means next to nothing. How much would a sirloin steak cost if somebody offered it to you on the street? What if your friend gave it to you? What if no steaks were available at a grocery store? Would you trust any estimate of a price when money is mostly meaningless?
Asking about purchasing power is also meaningless, you either knew someone who could get you stuff or you didn't. In a weird way, Soviet shadow economy ran like a prison: if you know a guy, you can get stuff, if you don't, you make do what is given to you or lie, cheat and steal to get what you need.
Also, official statistics would lie and as the lies travelled upwards, they would stray further and further from the truth. So no reliable statistics are available or possible. But you take what numbers you can find, ignore any you can't get, and claim that Soviet Union was somehow a paradise, thus commiting McNamara fallacy:
But when the McNamara discipline is applied too literally, the first step is to measure whatever can be easily measured. The second step is to disregard that which can't easily be measured or given a quantitative value. The third step is to presume that what can't be measured easily really isn't important. The fourth step is to say that what can't be easily measured really doesn't exist. This is suicide.