I would like "Killer" traits return

[Wobi]

I don't think people recall that Killer Traits in FFXI had a rather low proc rate and outside of a Beastmaster or Blue Mage were more or less worthless. Besides the occasional intimidation proc they also affected resistance rates of attacks and additional effects. Such as with Blue Mage the effect of a plant based attack that would occasionally apply the add'l effect: Slow. If the mob type was strong against the type association of the attack it was more likely to resist.

As for the elemental wheel, this was also based on resistances. Water-type mobs were more likely to resist a fire based attack, it could occasionally hit for full damage but would likely be resisted to half or even a quarter of the potential. This would obviously lead you to use a thunder based attack to ensure the likeliness of a full damage attack, it also increased the chance of a critical proc by a bit. As the elemental wheel is now split between Conjurer and Thaumaturge they would have to retool the entire story line and lore as well as reassign all the abilities for such a thing to be added again. This would also require every mob to have resistances or weaknesses to make such an addition more than a pointless gesture. I actually preferred how THM/BLM worked towards the end of 1.0 (or even before when we had Light and Dark based attacks) but given the pace of combat in 2.0 onward they would have to basically give BLM an infinite MP button or keep the astral/umbral flip to restore MP technique.

Honestly it's easier to balance things the way they have it, there is a reason that FFXI had only niche appeal and they were very forthcoming that FFXIV is not that kind of game and actively worked to simply certain mechanics to make the game more inclusive. Because the moment any class appears to offer an advantage over another in a particular fight you see class-stacking and "This job only" in shouts/party finder/etc. If you think otherwise we have 10+ years of data in FFXI proving this happens every time.