What's the point with that quite lackluster story in Endwalker?

[Brinne]

EDIT: Although, EW also seemed to be hinting that the Allagans may have created some beast tribes. One of their scientists was hysterical about the fact that Amon had given some random test subject the head of an elephant (possible origin of the Matanga).

It is confirmed canon that the Allagans created the Ixal, at least! Meanwhile, the Sahagin are apparently Echo-capable, so ???????

EDIT: Thinking about this further (for some reason), I think it's safe to say that at least generally, races/tribes that exist across the Shards are probably Sundered Ancients. Ones that are unique to a Shard, such as how the First had no Ixal, or the Source has no Amaro, probably have different origins, such as being familiars. Namazu were confirmed as existing in the First before the Flood, though, which would mean that it is likely that at least a few of the Elpis NPCs did, indeed, become delicious sushi.