Personally look at the Old One creations like a developer and you see this:
Version 1:
-Slaan - Efficient, powerful, built in natural armor and weapons, practically impossible to corrupt, functionally immortal, unfortunately they're significantly lacking in imagination and independent thought, useful as assistants but no more.
Version 2:
-Elves - Remove the natural armor and weapons, you can make those aftermarket. Downgrade the high end Slaan magic ability for a mass producible version with more imagination and personality. Unfortunately production is very slow, and you got unexpected problems when you introduce greater personality variation with a strong natural affinity for the Winds, as the Winds also reflect various psychological aspects, the elves get...eccentric. Very very driven, but eccentric as hell.
-Dwarves - So Elf personalities too unreliable and volatile, what if we turned the dial on emotional stability until the limit of where you can still have independent individuals. Unfortunately this kills their ability to work with magic directly, though they are very reliable, and very durable. And the production rate is STILL super slow.
Version 3:
-Humans - Okay, maybe we're asking too much to want each unit to run for a thousand years and do everything at once. Tone it down a bit and let them update their own software to specialize. Up the production rate a hundredfold. Unfortunately this makes them super error prone, just about anything can mutate them and if they try to do everything despite being made to specialize, they also mutate.
Version 4:
-Halfling - Lets up the debugging routines ALL the way through the roof. Sort of a success, but the dwarf problem happened again, most of the magic got debugged out, and turns out when you put that load on a human base template you get something smaller and physically too weak, AND still eat too much to boot. Lessons learned.
Version 5:
-Ogres - Big, strong, magic capable, very durable, lifespan problem mostly worked out without hurting production. They do eat quite a lot to support all that, but food is a solved problem. Lets roll them out-*Signal Lost*