For the sake of clarity, in the time of the Ancients was Cluster essentially a wandering artist that routinely auctioned off planets for food in place of growing food themselves and were the Watchers basically genocidal Anti-sentients in regards to the lesser races?
From what you can gather, the Cluster utilized evolution on a mass scale as a kind of skunkworks, seeding life on harsh worlds to then harvest the resulting adaptations, with most of their population, if you can call it that, living in space in nomadic cluster forms. The Watchers on the other hand are less clear, but seem to have been more artistically minded, viewing a planet's biosphere as something akin to a highly complex work of art, like a bonsai tree in need of careful pruning and grooming. Such garden worlds were likely not intended to hold any practical function beyond their simple beauty and artistic appeal, collecting all manner of interesting creatures, or even shaping and guiding evolution to make them more interesting, and micromanaging them in a carefully balanced ecosystem, like a fish tank or terrarium, but on a planetary scale.