Despite being a linker I don’t know about joint penalty and hangman’s knot for pvp. I can tell you that I never see monsters attack when I use it, I’ll have to pvp someone later to try it. It requires more than one target for it to work.
As for the quick cast attribute it isn’t exactly final damage but it works similar to how you think it does. Read this it should explain it better than I can. Good luck.
Edit: Also to explain aoe defense/attack ratio. Everything in the game, unless it has it’s own stated system, can hit multiple targets. If you have 2 aoe attack ratio and an ability says it has 3, you get 5. By default if the skill doesn’t say it has any it should have 1.
If you attack a group of small mobs that each have an aoe defense ratio of 1 with a skill that has a combined total of 5 aoe attack ratio you will hit 5 of them. If you instead attack of group of mobs with an aoe attack ratio of 2 it will hit 3 of them. The game reads the skills aoe attack ratio and subtracts the defense ratio of each mob struck from your attack ratio until it the attack ratio reaches 0 or below.
So if you were to go linker with hangman’s knot with the attribute to reduce aoe defense ratio by 5, you could theoretically hit all the targets you have joint penaltied and then some if there happens to be more in the radius. This includes ice bolt and ice spikes. This is the reason falconer c1 is taken, they have an ability called circling which reduces enemies aoe defense ratio by 5 which enables really funny things to happen with aoe attacks.