After reading the comments in the Hub, I think you have to explain the details better.
And I would like to give you my point of view, maybe it gives you material for a second article.
All the spawns come from a bag of Mon's with different % of posibility to come out. So, in every place could come out one of the 251 Pokemons. Only that, for example, the Legendaries have a probability in this moments of 0%.
But there are at least two types of spawns, the nests and the normal spawns.
The first ones are described and limited by Biomes, but this don't mean that there can't come out other Mon's, only that they have a lesser probability.
The second ones are more terrain-dependent, but again there can come out other types.
And in events the only thing Niantic do is changing the value of probability of the event-specific Mon's, without taking out of the game all the other's.
And reading the new article about time-of-day specific spawns of some Mon's complicates a little bit more the function the program calculates everytime when a spawn happens...