Corinnguard
Hero
Have you ever checked out the Aasimar and Tieflings from Pathfinder 1st edition? Both of these planetouched races in PF1 were given their own lore books in that RPG. Blood of Angels and Blood of Fiends. Sometimes a RPG does a great job portraying a race, and sometimes it doesn't. If it doesn't, homebrew it till you like it.Imho, that's not lore that matters or has much value.
That's FR-specific silly business. All of it pretty recent and forgettable and only existing because the FR is the gelatinous cube of settings. It's definitely fair to say that generally speaking, Aasimar lore is extremely thin and inconsistent. They don't reflect part-angels from mythology/fantasy literature (who are approximately a million times spicier than Aasimar) the way Tieflings do reflect part-demons from mythology/fantasy literature, for example.
By Mulan gods are we meaning Mulhorandi? Took me a while to unpick that one.
Honestly I blame 3E. It utterly ruined Aasimar and Tieflings, and only Tieflings really recovered. 4E having Daevas which were so much more interesting than Aasimar doesn't help (and the idea that they're "the same thing" as Aasimar is terrible and whoever thought of that should stop writing lore forever). I believe 4E much later added Aasimar and they were milquetoast as usual.
As for the Devas, if they were so much more interesting than the Aasimar, why didn't WoTC bring them forward into 5e?