Primordium and Prometheus spoilers below
The Primordial said that the Precursors and the Flood are one and the same…so this would mean that they’re the same thing. This leads to a dilemma: The Flood wish to consume everything, and they are obviously a disgusting green juice dripping slimy thing. Now how could something that doesn’t care about life, simply to make everything part of it, create the Forerunners and humans?
This led me to one conclusion: that, similar to Prometheus, the Precursors used their DNA to make the Flood, which would explain the Flood’s magnificent ability to grow into such an intelligent force (gathering information then eventually becoming a gravemind)
You could say, the Primordial was just a gravemind that was screwing with the Didact…but the Primordial was locked away for millions of years. Why would the Precursors simply put him there to screw with everyone? He also said “it is your task to kill this servant, that another will be freed”. So he obviously had a purpose.
What are your thoughts? Can’t wait for Silentium to reveal the answers.