From Dark and Darker Wiki
The wiki seems to be wrong in its wording, it ignores 15% of enemy's existing physical damage resistance. So if they have:
20% physical damage resist times 0.85 = 17%, you ignore 3% of their physical damage resistance
85% (physical damage resistance cap) times 0.85 = 72.25% = you ignore 12.75% of their physical damage resistance
Basically, Thrust is not good. It was nerfed. Against a Wizard with low armor, it does close to nothing. Against a fully armored Fighter, you get some use, but it's still not what I'd call incredible. You be the judge, though