A little reasoning:
What is Dagger | Dirk? The cheapest weapon in the game. It's main trait is that this weapon has a 0 cost. Other non-elemental weapons are stronger, but they come with a cost.
Why is this card ignored? Because the cost increase for Longsword is ridicule. Any deck that uses "other" weapons is obviously rushing, as that's the only thing those weapons provide: cost efficiency. But the fact that you are limited to ONE weapon slot makes most rush decks use either Longsword / Gavel / Longbow or Vampire Dagger / Arsenic, depending on the amount of off-element quanta they have and on their mark. Even if the mark bonus was changed to, say,
and
and
or something, this card won't see use over a Longsword, as one more damage is worth one more quantum.
What can be done to solve this problem? The fact is, if we don't alter this card drastically it's not playable. It can't outshine Longsword, and even if it did (say, 2|5 damage with the above bonus for
), we're not sure it will really be used because of auto-mulligan screw-ups (one quanta to get more good draws? I can see that happening). Therefore, we need a different solution. An ability is the only thing that comes to mind.
A possible suggestion: dual-wield (if you play another weapon when this weapon is in play, add this weapon's attack to that of the new weapon).
This would see some good use, at least in rushes. It might even be balanced, although I'm not sure.