EffectPoison() and EffectDisease() can only apply a limited set of pre-designed Poisons and Diseases per the relevant 2da files. Per nwnlexion, we cannot add new poisons or diseases to the game by expanding the 2da files; we can only edit the behavior of what's already defined.
This limits the modders ability to make custom disease and poisons wherein the effect DCs might scale by HD and/or caster level, for example. Also, these effects are pretty much outgrown at high levels of play by the limited range covered by the DCs of the predefined poisons, regardless of efforts to rebalance an effect here or there.
I suggest allowing modders to add more lines to these 2das to support custom poisons and diseases.
I also suggest adding new functions or updating the existing ones to allow the specification of all of the details otherwise set in 2das. Perhaps adding EffectCustomPoison() and EffectCustomDisease() functions is viable?