let's say that in this system a person with a computer finds one block per month. Then four people with a computer each should find a total of 4 blocks per month, right?.
Why?
If it wasn't clear, in this example the intention was that the 4 people aren't all there is, there are 4000 more similar people each finding 1 block per month, for a total of 4000 blocks per month. So again, if 4 people find 1 block per month each, then between them they find 4 blocks per month.
Why?
It is characteristic of non-parallelizable PoWs that they do not scale in the way you describe. I believe we have a misunderstanding here.
Let´s make it a bit easier: assume, as in Menis example, that 4000 blocks are found per month by individual participants, under the assumption that your non-parallelizable PoW is in operation. Assume further that all of these people just meet up and decide to share the revenue equally to smoothe out their income stream. According to what you have been arguing, the total number of blocks they find would go down to 1 purely due to the fact, that they are colluding in terms of revenue-sharing.
By definition 4000 blocks, will reduce to 1 by your formular magically devining social contracts?
Good luck with that line of argumentation...