I, too, feel there is a huge lackluster on the elemental weaknesses/resistance in this game.

The way I see it, the elemental resistance/weaknesses shouldn't be about damage but bonus effects.

For example, a fire monster/boss. So attacking it with its opposite could give a small perk, such as self-heal penalty, a slow effect, etc.
An extra effect you wouldn't get otherwise. And that effect would tip the fight that much would still help a bit (especially considering the monsters/bosses build up immunity).

As for players, same. Boosting an elemental resistance would also boost a status resistance (sleep, slow, silence, ...)

That would allow to have a more meaningful elemental feature in the game, while leaving it somewhat underpowered as the developers wanted (and some players want).

Simply hovering your cursor over the element in your profile window would display which status is tied with what element.

What do you think?

N.B.: Also, by being able to pick up attacks from other classes, it would allow other jobs/classes to have access to some elemental spells too. So it wouldn't be restricted to BLM/WHM.