The problem with the splash poison combo is the you are still FORCED to use one of the 3 attribute slots on direct damage.
If you could get the flask to do AOE damage, poison, and heal or shield, it might be more useful.
Also, since, from what I can see, there is a max of 2 enemies, the AOE is sorta wasted, if you could splash poison 3+ enemies it would be cool, but since the moment the first enemy dies the aoe becomes useless, it's just not worth it.