Ragnarok Online 2 Poisoning Weapon calculations

I'm planning my assassin build, and I see that everyone keeps the skill at level 1.

I'm currently unsure how the skill works exactly, but judging from numbers:

Level 1 - 10% damage every 2 seconds for 20 seconds = 100% damage over 20 seconds
Level 5 - 15% damage every 2 seconds for 20 seconds = 150% damage over 20 seconds

Isn't a 50% damage boost a big deal? Seeing how most offensive skills are around the 30% damage range.
Or how is that % actually calculated? Is it calculated differently?
Does the poisoning work on all monsters including bosses?

Maybe people are overlooking a very good skill. 

Actually it's not bad from raid & dungeon single target DPS perspective, but you can afford to leave it at lv1 until you reach Lv45+.
Theoretically (still in progress) Lv5 Poison damage deal more like 5.63% increase to your overall DPS to Boss (that can outlive 20 secs) compare to Lv1.

In current state of Damage Per Minute, Rogues are doing:

**Ignoring
1. White damage
2. 3 seconds animation Dance of the Moon
3. Haste & Vigor stats
4. Unstable Doping
**

1. Poison Damge @ 10% every 2 sec (5% per second)
2. 60% 5pt Deadly Strike @ every 6 seconds (~9 hit per minute)
3. 9% of Combo Mastery proc 5pt Deadly Strike @ every 1 sec (proc from skill), which is about ~5.4 hit per minute, round down to 5 for easier calculation)
4. 25% Double Attack @ every 1.0 sec (60 hit - 9 Deadly Strike - 5 Combo Mastery = 46 hits per minute)

Deadly Strike + Combo Master = 14 hit per minute
Therefore Double Attack = 46 hit per minute
Both benefit from Crit, assuming at 25% Crit rate for lv50 (someone let me know what is the norm crit for lv50 Rogue)
Assuming 95% hit chance, ignore mob's dodge.

Skill................Hit..Crit...Hit Chance...Total %Damage
Deadly Strike 60%....*14..*1.25..*0.95........1366%
Double Attack 25%....*46..*1.25..*0.95........998%
..............................................2325% (TOTAL SKILL DAMAGE PER MINUTE)
..............................................39.39% (TOTAL SKILL DAMAGE PER SECOND)

Poison Damage.......Per Second......Total
10% every 2 sec.....5%..............39.39% + 5% = 44.39%
15% every 2 sec.....7.5%............39.39% + 7.5% = 46.89%

Lv 5 Poison 46.89% compare to Lv1 Poison 44.39% = 5.39% increased. Which is still quite a lot, but IMO Unstable Doping should get the priority over Poison although I'm still lazy to calculate. Unstable Doping would add <20% overall (20% chance of proc over skill, therefore at least 2 proc over 1 minute) & benefit poison damage but Crit buff would favor more on all damage except poison (inc. white).

Dancing of the Moonlight is just personal preference consider 110% damage @ Lv5 for 3 sec animation vs 60% Deadly Strike + 2x 25% Double Attack (2 more combo points). Deadly Strike should have higher DPS in long term (considered chance of miss in short term).

Any mistake I'd done please correct me.