I'm thinking along different lines.
I'd speculate that the Praeses aren't as evil as Alice thinks.
Here's why. Imagine Earth pre-Blink. AI faction and biotech faction about to go to war. No alien encounters mentioned at all. Then suddently, all the AIs vanish and the Earth is instantly edited. At the same time, a bunch of orbital habitats instantly appear. This is the action of a godlike intelligence with (at least weakly) godlike powers. Let's call it "Bob". Bob is the Singularity, an AI that has figured out how to improve its own intelligence, then repeat the process, until it's smart and powerful enough to easily shape worlds. Bob eliminated the other AIs before they figured out how to compete with him.
The Praesides, whether they appeared that day or sometime not long after, were not players before. And they've taken the name that historically means "governor of a province". I'm guessing they were living out their own intelligent treelike lives elsewhere in the galaxy, and Bob, before Blinking everyone, found them and cut a deal with some of them. He offered each one a chance to govern a new colony (or part of a colony) of intelligent but naive colonists, to have free reign in their education and care, in return for something they wanted. Some of them agreed, and got Blinked into place on a colony asteroid.
They're governors, and whatever it is they want, they got it, 5000 years ago. Presumably as treelike things, they're pretty long-lived and patient. They don't move around on their own, so conquering another planet doesn't seem like a priority. They already share their colony with a few other Praesides, so they're not really aggressively power-hungry either, or there would be just one left on each world (and that's not what Gavia implies.) Also, the colonies are not overpopulated (or Ardent would come from a scarcity economy, which he evidently doesn't!)
So from the Praesides point of view, they're doing what they want to do, and educating their charges to their own tastes. Their world is pretty much utopic. I think if they sent Ardent to upgrade Earth's technologies, they did it from altruism, thinking the Earth people might want to have nice things too. (Alternative suggested by a friend: Or they just got bored! Also likely.) The Praesides are likely naive, well-intentioned, and therefore dangerous exactly the way Ardent is -- because they don't think about unintended consequences.
My guess is that Bob wouldn't approve of this move, but never actually told them not to. Instead, Bob moved to the Moon, and placed the Nightwalker on Earth to send him a signal if any really higher technology appeared there. Which just happened.