Part 2 of this Theory

After the events of Endwalker like you suggested with Hydalyn now gone and the barriers between shards possibly weakening maybe this reflection of the WoL then went on to attack the remaining shards to absorb their reflections and now comes to the source for us seeking to absorb us and become immortal so they can rule over all Shard's forever and ensure the peace and security that they and their companions once strived for but sadly their companions did not live to see will never fade with an unworthy successor. As for the magiteck you suggested perhaps it was created by this Shard's version of Cid who was one of the few companions of this Azem shard who survived and who takes on a role much closer to his FF XII version, maybe even having a somewhat similar but different version of the Iron Works moto, this time being, Peace or Security through Technology. We naturally defeat them by unifying the people of the Source (it would have to be after we have visited most of the Source) and maybe the first as well through inspiration and example and not force and defeat them through the power of friendship, maybe seeing the sight of of us with our companions gives our reflection an emotional flashback to their friends to further up the feels. I know this is really fan servicey and a tinfoil theory at this point but i just think it would be interesting.