Do we have any poison weapon appart from the narthecium

Just the Narthecium, as far as I'm aware.

So best element and we get none of it?

That's one of the best self-setups for ridicule I've ever seen.

It's not like Eldar get any poison either outside of the scorpion lashsword

And Orks only get poison from the painboy

I dunno about best ailment. Poison and Ablaze hardly seem with it, most of the time.

EDIT: While I would like to see Hellfire rounds in the future, I think we have enough toys for the time being.

Which is what OP doesn't seem to realize yet So in the spirit of informing: The status ailments only reach dangerous levels once you applied so much that the application process itself already killed the target.

Exception is if the source causes no direct damage, such as walking into a Tyranid spawning pool.

It does make a difference if you meet someone who is not at 100% Health, you got a chance that the ailment may kill that fella.

On a 100% Health enemy, you take the same ammount of hits to down him

Now I won't claim that a melee Apothecary is anywhere near as effective as an assault loadout, but it has a unique advantage: You can take the Narthecium and a Chainsword (or Crozius Arcanum if you're a WP) and just spam attacks at the enemy, when one weapon breaks you can simply switch to the other.