I’d say it’s slightly deeper than you’re thinking. The problem is that elemental damage is bad and thus it needs set support, not just gear support, to make work.
The reason is resist reduction. Having your damage type split into 3 makes it harder to get a lot of resist reduction for all of it. Focusing on one damage type makes it easier to acquire a lot of resist reduction. And you can’t just put equal amounts of elemental resist reduction into the game as singular fire/cold/lightning resist reduction or the elemental gear will start out-competing the fire/cold/lightning gear.
On the flipside if you just make a few really strong +%elemental damage pieces, it will STILL be better for a singular damage type because +%elemental damage boosts all 3 damage types equally, so you just pick one and ignore the other two. +100% elemental damage is +100% fire, cold and lightning. But +100 elemental damage is 33 fire, 33 cold, 33 lightning.
So Elemental Discord Cadence would probably require a set to support it, and even then depending on how the set is designed it might still end up being better for fire, ice or lighting cadence lol. Really. It’d have to be a restrictive set that uses up multiple key slots, like the weapon slot, the helm etc. And its elemental power boost would have to be loaded hard into its set bonuses as opposed to on the items themselves.
I was also resistant to the idea of the new Lightning Discord Cadence in the playtest, but I had to concede that attempting to make elemental cadence work… wasn’t working.
So none of this as cut and dry as it seems on a glance. Make Discord just add flat elemental to cadence? Physical builds will just convert it back via beronath sword. Make Discord 100% phys to elemental conversion? Singular elemental types will outshine elemental cadence every time, going against the very theme of the transmutor. And themes matter a lot to the devs, (with some good reason!)
That’s why my suggestion was to learn to live with this change and request an elemental cadence set.
edit
See Belzak gets it. One really clunky thing you could add to the game is 100% of elemental damage converted to elemental damage. This would make it so it’s impossible to stack one elemental damage type, locking you in to true triple elemental damage. But the issue is this wouldn’t fix Discord.