Hey, I noticed that Ranger's poison passive is, uh, scaled cubic. It takes about 7 or 8 levels to get a 10% DPS increase, but below that, it's negligible.
Chance * Duration * DPS = average poison DPS. (This could be lessened if the duration exceeds the time to reach the end, but smart targeting can easily avoid this)
Cubic scaling that's balanced at the high end ends up being a pitiful one-point skill. Compare with the dragon's poison - a single skill gets ~50% damage for investing a single point, and an additional 6% base damage per skill point. This is completely linear, but fairly balanced.
The ranger should maybe start with one or two poison stats maxed at skill level 1, and the others should stay in the current state or start somewhere in the middle. The question is whether it should be a strong effect that doesn't happen often, or a weaker effect that's more consistent. I'd rather start with the chance higher, like 5 or 10%, keep the duration at 10, and maybe let just the damage per second scale up. I'm not sure that it needs a buff at higher levels, but it is basically a trap if you give it anything less than 100% at the moment.
(Bleeding is more complicated because in theory you could max Bleeding and make that character play a support role. Similar principles may apply, but the case for buffing lower levels of Poison appears stronger to me.)
(Also, I'm not sure if critical strikes affect the poison damage for that strike in the event where both effects trigger)