So we do not know who the Harbinger is yet in Halo Infinite but apparently it has some ties to Banished if it assisted them to some extent. This may sound a bit off but what if this mysterious being is actually a Precursor who came in to stir things up for the humans using the Banished similarly to how Primordial did with the Ancient Humans using the flood. Harbinger does mean “something that comes before or foreshadows something to come” and is synonymous to the word, “Precursor” so why not?
I sincerely doubt it. The primordial was corrupted by the flood, hence the morbid fascination with humanity. Also the precursors held the mantle deeply but also believed wars were neccesary so, unless the banished were actively killing off humans with extinction in mind, they wouldn’t intervine (if they did itd be on our side anyway). Or be involved. Unless they were primordial 2.0 but they’d just use precursor technology alongside the flood to consume the galaxy.
Other possibilities of the Harbinger are the oh so mysterious meddlers, a forerunner, or more likely a contender class AI (my personal belief). Once factoring in BOTH definitions of ‘harbinger’.
Not to say your wrong, we don’t know yet. Anything is possible. But I’d also rather 343i keep the precursors a mystery (they are illuded as God like entities, mystery adds to this illusion).
Most casual halo fans don’t know what a precursor is so I doubt they might appear in this at least as a main line threat.