The problem in such logic, as I see it, is that the atonement of Christ was not suffered cumulatively, but vicariously, prototypically. For Christ's passion to be effective vicariously for any individual whatsoever, it would only have to be sufficient for the very worst individual that ever lived. Adam and Eve were prototypically the best that mankind would ever be, Christ on the cross had to be prototypically the worst that mankind could ever be. So the cross does not have to "mathematically" reflect the sum total of all punishment against sin, it merely has to be sufficient to encompass the very worst individual any individual could be.
Really, we're not all that different from one another. Our conceptions of degrees of sin and punishment are a bit stilted, imo. Does being Hitler or Stalin, and missing out on God differ substantially from being grumpy Uncle Charley who refused to believe in Christ and missed out on God too? The Lake of Fire may have warmer eddies in one spot than another, but how much does it matter when one is swimming in fire and drinking flames? If there are gold medals awarded in the race to hell, they can only be made of fool's gold.
What the atonement had to be in order to be for all, was sufficient for any sinner to gaze upon it with faith and say, "that was me." We aren't saved in groups but as individuals, the atonement of Christ was masterfully fashioned by God to work perfectly in that regard. It does so because it functions vicariously, not cumulatively.