AT LEAST it should gain "deadly venom" skill, which adds 2 poison counter on each successful attack.
I compared those cards, here are my thoughts:
1. Poison is cumulative.
2. Poison lasts even after the creature is killed.
3. You can poison a stronger creature, which will be able to penetrate shields. Deathstalkers have Deadly Venom, but most shields are unpenetrable for them.
I'm afraid 2 poison would be a little OP, so I try to preserve balance here. Let's hear other members.