I got hanzo breaks a while ago but since he is only used in my ranked team this has slipped my mind, but as far as I can tell strong poison is no different at all to regular poison, the damage is identical and any technique that removes regular poison removes this just as easily, so my question is what is "strong poison" supposed to do?

Its explained in a different post, but Strong Poison in this game is like another debuff. The poison debuff can only stack 4 times. Strong poison is another debuff so you can stack them both on top of each other. It also helps when there are ninjas that 'remove one layer of debuffs' they will remove one of the poisons but not the other.

You get the most use from this using poison tai teams of water main. But its not that useful with all the immune ninjas in the game. Would have been better if Strong Poison could go through immunity.