The Azerite armor from normal atal'azar and other lvling dungeons is ilvl 280 but without secondary stats. So for a 250+ ilvl mythic item with secondary stats it might not be an upgrade (considering some of the azerite traits are useless for lvling as a disc priest etc).
Or am I speaking nonsense? ( I know the secondary stats start dropping in value fast as you gain levels).
As someone with Mythic gear who quested in beta I had replaced all of it at or around 118. Even the Pantheon trinket, which at ilvl 265 gets replaced by quest greens around 117 assuming you aren't going to be making use of the proc, which only goes off if you have all other pantheon trinkets and even then results in a huge raw stat loss if used at 120.
I don't think you are understanding. The traits are grayed out yes, but Relics also offer +x item level to the weapon. Look at the tooltip on your relics. You can still get relics and put them in the relic slot and get an ILVL increase. If you remember, artifacts are only ILVL 152 (750 before squish). The relics are how they are able to be improved ilvl wise. Yes the traits they offered are gone, but the relics still increase the weapons overall ILVL, so the relics are absolutely still useful out of a M+ cache