There is tangible lore behind the Progenitor tier stuff. All tier sets are canon according to Chronicle, and ontop of that, the Sepulcher armor is described as us "harnessing the power of the First Ones"
"Harness the power of the First Ones by collecting distinctive class armor sets via raids, PvP, or Mythic+ dungeons. The Progenitor armor set will grant your character new abilities based on your specialization, and includes a helm, shoulders, chest, gauntlets, and leggings with 2 set bonuses. The first set bonus is unlocked when two set pieces are equipped, and the second bonus is unlocked when four set pieces are equipped."
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Yeah, and Argus' soul proceeded to get clapped by ONE of these heroes in Zereth Mortis, showcasing our growth in power thanks to the Shadowlands amps.