As it is now if I am correctly:
Burn inflict 3 damage on a 100% chance rate every turn. 10% that it will worn off.
Poison inflict 0 or 1 true damage every turn - 50/50. 10% that it will worn off.
Both effects can kill.
Burn looks more than a little stronger than Poison after a 2nd thought, as it is now. When that is said looking at the skills of the differently troops it looks for me that Burn was made to be stronger than Poison, and there would be needed a ton of balancing work on troops if poison was raised. There is some poisonous troops that poison every enemy troops, while the best burn skill we find in Salamander that has a 30% chance to burn every enemy troop.