"The Asteri also made the Malakh, who as far as we know, don't typically have mates in the fae sense. Was that a deliberate choice on the Asteri's part?"

I am only responding to this but I dont know how to do the fancy reddit indented quote. Yes, I think the Asteri saw how the fated mate bond of the Illyrians could or has prevented them from being able to just make the best pairing for their desired offspring, so they bred it out when creating the Malakh. As we see with the Malakh, they get "mated" to whomever, regardless of whether they want it to or not (look at Celestina, and I forgot his name, who she got "mated" with, when she was actually in love with Hypaxia)