We still don’t know why the main source formed in an underground cave in Romania which isn’t even close to the source of Progenitor.
Viruses are too exponential in nature to set boundaries for themselves. Even now we are still experiencing another global pandemic. Any viruses spread, mutate and then eventually die. This is the viral life cycle.
It's the same with the Progenitor Virus. This is a relic of the "RNA world", which should not have survived since those prehistoric times, but survived because it found its "cradle" in these flowers.
In the Resident Evil universe, viruses have driven the evolution of all life forms on the planet. The virus that Alexia found in the queen ant even contained the genetic information of the mantis. Similarly, genetic information that is similar to that of extinct fish of the Permian period was transferred from the Abyss virus to the Scagdead enemy, which caused a characteristic cellular mutation:
Why haven't Lickers changed much after being infected with the Progenitor Virus? Because these creatures have reached their evolutionary dead end, so the virus has nowhere to develop them, except to enhance their sense of smell and reproductive system.
And why is the Progenitor Virus called this way, and Spencer mentions it in that letter to Miranda as "the key to evolution"? Previously, it was called the Clay Virus, as if referring to Prometheus, who created people from clay. Or, although it's an English thing, it was called the Mother Virus because mothers give us life.
This is the virus that caused
everything. And that's why it can work with people, animals, plants, fungi, and so on. No real virus is capable of such an interspecific infection, because it needs a certain compatibility with the host. But the Progenitor Virus was compatible with such a huge variety of life forms.
The developers also chose Africa as a place of events for a reason. They referred to the hypothesis that this continent was the place where humanity came from, and the tribe that lived there could even be older than the Sumerians.
So yeah, I agree that the Plaga parasite may be related to the Progenitor Virus. Especially when we see their remains in the kingdom.
But no, I do not agree that mold cannot have a connection with the Progenitor Virus. If we recall the effect of the virus on the leech, it taught the animal to steal genes, thereby the leech was able to absorb the genetic information of Marcus' corpse and get his memories and thoughts.
Surprisingly or not, this is the same thing that mold does. Each intracellular fungus steals information from the cell. And Miranda's abilities on katakana are described in the same way as those of leeches.
I mean, she's basically the Queen Leech both in terms of biology and in terms of referring to the Jesus character.