No swapping in weapons from your inventoy in a fight and poisons become instant-spells with a shared cooldown-timer
So how about to not be able to switch weapons out of your inventory into your active slots if you are engaged in combat. (you still can swap bewteen 1-hand/2-hand/Range of course)
It seems a bit silly to me, that it is considered advanced gameplay to have dozens of weapons in your invetory to apply every kind of poison in a fight and to swap then through.
If you would have to consider, which poison you take into the fight, I would say this is even a higher level of skill and will reflect more finesse of all the sneaky people.
But since this would just be a nerf for a cool class, I want to offer a second idea along with it, and yes, this is proably even to complicated to implement or to change game-system-wise, but let's see:
instead of coating weapons with posions, the poison line receives poison-skills instead. So at lvl 1, you get a spell aequivalent to the lvl 1 poison-effect. It is an instant spell and all posion-spells share a global 5 second cooldown. So regardless of the weapon you are using, you can "cast" a poison-instant every 5 seconds. So over the duration of the battle you can still apply all the things you want/need and don't have to litter your inventory with weapons and poison-flasks.
- poisons are instantly cast.
- An activated poison will apply with the next successful hit (melee or ranged).
- after casting a poison, this type of poison has a 20 seconds cooldown.
- you have a global cooldown of 5 seconds for every poison after casting a poison spell.
- the applied poison will last until triggered - so you can still pre-buff yourself with your prefered poisons.
I can imagine to limit the maximum poison-spells active on one target at the same time are depending on your hardpoints into the poison tree.
Hardpoints in Poison // Number of active Poisons
1 // 1
10 // 2
20 // 3
30 // 4
40 // 5
50 // 6
If you apply more poisons to the target than you limit allows, the oldest poison fades.
With this, you can still have the debuffs on the target, you really need to have to, but you are also flexible to change them if needed. This would also add some tactics to the system.
I think this system would give enough control over effects, but also give some restrictions, plus it would get rid of weapon-swapping-hell as well.