Status update
Added 2018-04-17 02:52:24 +0000 UTCOk, I'm certainly onto something, but so far the precision is way below what I wanted it to be.
Here is an example of a dataset calculated based on the new method without using any data from Steam API at all.

While it certainly seems to work on small and medium-sized games, the precision on big titles is really terrible.
Also, reliably calculating the margin of error using this new method is rather difficult.
Will keep you updated.