If you use Traitor (as Atlanteans) or the Communal Hearth (as Greeks) to convert Egyptian, Japanese or Aztec human units they don’t get upgrades like Greek, Norse, Atlantean and Chinese units would.
It would logically make sense that all Infantry, Cavalry and Archers are affected by the Line upgrades since those units clearly are those things and the upgrades work perfectly for the other civs that also have them too.
It would not impact the balance of anything else since Egyptians, Japanese and Aztecs don’t have those technologies but they also don’t have any means of converting units. Neither the the Norse that are missing the Archer line upgrades.