I know I'm replying to a dated post here, but we see the religious affinity of the Kett in indoctrination and exaltation and we see the wide variety of base species who are exalted. I don't think we'll ever know what the original Kett was, whether it started as a religion or as a species, but it's almost the bioengineering equivalent to the Borg assimilation from Star Trek.
The Jardaan we see similar bioengineering skill and technology, but the evidence we see suggests they are either creating a new worker race (like the Quarians did with the Geth, just using biological constructs as opposed to synthetic ones) or creating the next wave of their own species. Centuries of isolation from the Jardaan could have caused refugees they left behind to adopt a new social system and culture where they identify as something entirely separated from the reality of their original species.
We saw the Angaran helmet in the downed Remnant ship on Havarl that was hit by the Scourge, and the Angaran talk of time before the Scourge. To me that suggests they ARE Jardaan, but the pods filled with incomplete Angarans on Khi Tasira suggests they were intended as workers and the slight differences in representation in the statue discovered in "Forgotten History" that "suggested it may be a deity carving" to Avela Kjar may actually have been their progenitors who with slight modifications to the genes became the Angara.
Personally, I think the truth about the Jardaan-Angara connection lies somewhere in the middle of those two fields. Whereas I see the Kett as a separate entity with no shared history other than perhaps having 'assimilated' some Jardaan into their ranks. If the Kett were both the Angara and the Jardaan, they would've had the genomic data for the Angara and not been in awe of the bioelectricity of the Angarans, as shown in several datapads and audiologs.
If they had previously had run-ins with the Jardaan, and the Angarans ARE the Jardaan (with slight genomic modifications) ; however, it would explain why the Archon was so certain that the Moshae knew how to work Meridian while he had her captive and why they were unfamiliar with the bioelectricity aspect. But it would leave the question as to why the stasis fields on Havarl ONLY affect Angarans, as mentioned by Ryder in conversation with the Initiative scientists who join Havarl's scientists at Pelaav Research Station.
