Yeah, pet builds are best at stacking poison due to the large number of hits a target can get. But if you ignore pets, ignites are probably the easiest to stack (as I mentioned here).
My only concern about that is that removing the per stack damage increase strips poison of it’s unique effect, then the DoTs (well, bleed, poison & ignite) all become a boring beige with nothing to differentiate them. Which DoT would you like to apply today? Beige, off-white or oatmeal?
If you give the other DoTs a unique and useful mechanical effect then people will use them & find them more interesting, to an extent frostbite already does this as it applies protection reduction per stack. I also think that the other DoTs need more support from uniques in a range of slots.