I think that the Servitors may actually be some precursor to the Guardians Ghosts, but where a Ghost seeks out a single individual to essentially make immortal until the ghost itself is destroyed, the Servitors do the same thing but for many individuals. It is pretty clear that the Fallen were visited by the Traveler at some point, and that they were used by it to battle "the darkness" so it would not be a stretch to assume the Traveler created some form of "proto-ghost" to aid its Fallen Guardians. I believe that the Fallen are most likely kept alive by the same sort of "light" that a Guardian is kept alive by, though the light is spread through many of them. Which is why one Guardian is so much more powerful and has so many more abilities than even the most powerful of the Fallen. It was interesting for me that in the mission on Venus where you board the Fallen ship there are no Servitors around, but many of the screens show what appear as schematics for them. This could mean that the Primes are the "real" Servitors and the smaller ones are ones that are produced by the Fallen. Its also interesting that they are called Servitors (meaning Servant) while also being revered with almost godlike status (at least the Primes). This makes me think that the Servitors are in fact mindless automatons and essentially enslaved tools used by or modified by the Fallen. Perhaps that is why the Traveler left the Fallen. It gave them these things that gave them eternal life and they took the things and either fiddled with them to have control over them or straight up reversed engineered them into creations of their own design. Maybe what the Guardians perceive as reverence for the Servitors is actually just the Fallen placing incredible importance on them, and why Servitors seem absent from Fallen VS Fallen conflict. Maybe that is how the Queen of the Reef first took control of her Fallen, by capturing that which ensured them eternal life, and as such they had no choice but to fall in line and under her control. I always like how looking into the cards and the hidden backstory makes one feel like they are actually a Warlock of the Tower scouring through tidbits of data that has been discovered lol :P