I think people are confused. Life siphon skills have 2 components, the damage component and the heal component. They are 2 separate figures. The healing component of some life siphoning skills is affected by healing power, but it does not affect the damage component. So there is no offensive power gained from stacking healing power.
Bottomline is right now all life siphoning traits do not scale with healing power, which does not make any sense. Fix these traits (along with bloodthirst not affecting all life siphoning skills either), and then we can talk about more drastic changes if necessary.
Not true, just like in the original game, the prime definition of life siphon (vampiric) deals 25 additional damage and then gives you 25 hp pre hit at level 80 being a single component of transfer, Signet of the Locus works the same since it heals for a base of 936 hp at level 80 pre target, despite the additional heal component being 778 because the first 158 is actual siphoning, same with wells and on crit siphons. Ironically the Dagger Life siphon isnt a actual siphon but a 2 component spell that heals upon tick check ignoring if it deals damage while the other skills if blocked dont heal for the siphon. Currently some scale of healing power, some from power and some dont scale at all past your current level (or the fractal/other level 81+ zone bloodlust bug).
The definition of siphoning life is simply dealing damage while being healed at the same time. There is no hard and fast rule saying these 2 figures must be equal. In fact all siphoning skills have both a damage and healing component that are separate, just like I stated. If they were tied together then you would get healed for doing more damage (e.g. crits), but you don’t.
It is the 3 siphon-related necro traits that do not scale off anything (neither power nor healing power). This is what does not make any sense as healing-related traits from other classes scale just fine with healing power. The viability of siphon is mostly revolved around these skills because there really aren’t many siphoning skills in general (really only the dagger 2 skill, the others are underwater/downed skills or combos finishers and other misc sources).
Once these 3 traits are fixed to scale then you have to look at the degree of scaling. If the GW2 wiki is correct, the dagger 2 skill scales at 1/25, or .04/tick for 9 ticks = .36. The most comparable healing skill is the Ele’s cone of cold, which scales at .32. While there are various differences between the 2 skills this gives you the impression that ANet’s thought process was the scale siphoning roughly along the same degree as healing skills. So if they scale the siphon traits along the same lines as similar healing-related traits then we might actually see Necro’s spec into the blood line and gear healing power every once in a while.