Decimating strike should work on first hit, not when hitting monsters on full life

Hello, I've been playing the witchhunter recently and the decimating strike node really infuriates me. Why is it that decimating strike only works on full life enemies?
All damage overtime effects renders this notable useless, even the expedition tablet that removes life from monsters. Why cant decimating strike proc on first HIT instead of full life? Even in endgame content reveal video Jonathan stated decimating strike works on the initial hit against enemies, so why isnt that the case?!?