Honestly, I'm not sure Toxicon is crap, so long as one thinks there should be damage-refunding (only) for certain heals. It does more or less what you'd expect: softens the cost of shielding, while thereby further punishing any at-cost sustain that is not a shield.

I just think the (lack of) shield-stacking functionality is crap, and the lack of any other way to generate Addersting seems a bit of a waste (even if it were as simple as generating a stack every 20s passively, akin to Addersgall).

Had I my druthers, sure, I'd tear the mechanic out root and stem and replace it and its surroundings entirely, but...