>>3774835>In FFXIV, fire spells hurt Bombs instead of healing them.Things would get incredibly messy if you started involving things like elemental resistances when many classes have elemental attacks as part of their kit and rotations.
Black Mages primary damaging spells are all fire based.
Pictomancer has some spells in their chains be fire based.
Gunbreaker has a lot of explosive skills as their big damage ones.
Ninja has several fire based attacks.
Summoner has 2 fire based summons and they rotate through their summons, not pick 1 and stick to it.
Machinist has bombs and other fire based weaponry as part of their basic attacks.
Elemental based resistances would overcomplicate things and most likely force attacks to be non-elemental or always have alternatives that wouldn't have a big impact on their basic playstyle or performance.
Many RPGs or JRPGs can get away with that since they usually just have normal attacks (usually auto attacks or a single normal attack) and then spells. That structure wouldn't really work in an MMO unless you completely revolutionized how RPG combat is done, for no real good reason.