Is Tenacity relevant in EW?

[Seraphor]

So in other words it's a trash stat to meld.

If you're doing Savage? Yes

If you're not fussed with Savage and play more casual content?
TEN can be useful. The difference in dmg between fully melding DET vs TEN isn't all that big, TEN provides 75% of the damage that DET does, and melding in general is already just icing on the cake anyway.
But as well as 75% dmg increase, you also get comparable defence increase AND increased healing received, so the survival benefits are twofold.
Survival benefits that don't matter in Savage, but do in dungeon pulls.

Not everyone does Savage, and of those who do, not all of them Tank Savage.
I for example love healing casual content, but wouldntdare heal Savage, which I'll only do on Tank or DPS.