• It isn't specified how many parts everything was divided into when Hydaelyn sundered the planet; presumably they were all split into 14 like the planet itself, but given three Ascians were somehow able to escape it's not unfeasible that not everything was divided so evenly. However, unless we are told otherwise it is best to assume that yes, other than the three Source Ascians (Lahabrea, Elidibus, and Emet-Selch) everything was diluted to 1/14th of its original aetheric volume (including the PC's soul).
  • If the PC's soul was evenly split into fourteen, Ardbert rejoining with them would not make them compleat again.
  • This act serves mostly to repair the PC's soul, which was in danger of collapsing due to the primordial Light they'd absorbed from the Lightwardens throughout Shadowbringers. There may have been something of a power boost, but it would not be enough to fully close the gap between you and Emet-Selch / Hades.
  • The rejoining was likely permanent, and was almost certainly the entire reason Minfilia denied letting Ardbert help halt the Flood of Light.
  • Emet-Selch seeing the PC as an Ancient is probably meant to bring to mind that, to him, they are beginning to echo the power of eld (at 8/14 soul fragments, they are likely the most compleat individual the Ascians have seen in eons outside their own group).
  • The PC being a reincarnation of the fourteenth member of Amaurot's governing Conclave hasn't been confirmed, nor has that fourteenth member been confirmed as one of Hydaelyn's summoners. These are just popular theories.
  • Referring to the PC as the Warrior of [Light / Darkness] is probably not particularly meaningful outside of denoting their particular role in that territory (the PC is the Warrior of Light on the Source because s/he needs to drive back the dark, while the First needs (or at least needed) someone to rise up against the Light).