The end boss of e12 was Artemisia/Ultimecia just not in a form we were expecting. Eden's Promise is based on a statue of Artemis and Oracle of Darkness uses many abilities that originated in FFVIII's final boss battle with Ultimecia.
Chemist was for the most part the result of a red herring that concealed that the actual job hint in 5.3 was in the G-Warrior fight.and many were convinced the 4th healer would be Chemist, with strong "hints" for both ingame.
Some thought we would be getting dancer due to misinterpreting Lyse's dress and kata as the garb and movements of a dancer. A lot of people were actively pointing that out as wrong.In Stormblood we thought we were getting dancer, but it turned out to be nothing to do with it
We did become the Warrior of Darkness fighting to take back the night from the forces of light. The assumption of a evil/corrupt path was where those speculating went wrong.and in Shadowbringers we thought we were literally becoming the Warrior of Darkness and going down the dark/corrupted path yet nothing of the sort happened.
Sage is hardly a new class (the name originated in FFIII as the final and most powerful caster job) and the Nuoliths are not really original nor unique being based on a reoccurring weapon system in Japanese fantasy and sci-fi media (the Gundam meta series' bits/funnels/dragoons/fangs have existed since 1979).Enix like to go out of their way to avoid the popular assumptions and "surprise" us with something different. For the healer they even went out of their way to create an entirely new class with a completely unique weapon.
With the shirt reveal they played up and into the Dark Knight and Necromancer speculation. It comes off, along with them pointing out the irregularity of the Maiming gear and the unknown job being a melee dps, more as an attempt to point the player base in a specific direction rather than truly obfuscate.I'm almost certain it won't be Reaper or Necromancer. It will be something no one expected. Possibly even another entirely new class unique to FF14.