Job identity loss in FFXIV IMO is a result of the game pretty much abandoning the RPG part of MMORPG.

Generally in RPGs all enemies aren't made equal. Enemy types would have different elemental weaknesses/resistances/immunities/absorption. Different resistances to physical damage whether it was all physical damage or just specific types like piercing, slashing, bludgeoning, etc... This at its core would make certain characters/classes/builds excel against some things but fall behind against others. RPGs would also promote horizontal progression options via gear in the form of set bonuses, added effects, skill bonuses, skill augmentations, etc...

FFXIV has gone the route of removing all build diversity and replacing it powercreep making raw stat numbers bigger while trying to make it so every job within a role type has the same tool kit.