This thought just occurred from reading info on the Archon. Starting off...
The Kett send armies from their own Home world to locations in a galaxy alongside an Archon to gather data and send new species for Exaltation. Only 2/3 we know of; Milky Way, Andromeda and the unknown galaxy the Kett come from (unless the Homeworld all of a sudden gets revealed to be in Andromeda).
We have been away from the Milky Way for a long time, more than 600 years. Could the Kett be residing in the Milky Way too? Before anyone debunks this, let me explain something.
Yes, the Archon (the one we face in Heleus) is a Kett leader but not the highest in the ranks to be the entire ruler of his people. Plus, his goal is to exalt species and gather data from Heleus. If the Kett are in the Milky Way, then they won't send info on Humans, Quarians, Turians, Volus, etc to other Archons, instead it would go to the real boss, the whatever of all Kett. The Archon finding us in Heleus would also just be irrelevant data as the Homeworld would already know.