I guess it's completely broken. Tested 20% RI vs 25% DR + 40% Tenacity in IWD (without boons, buffs/debuffs, feats and others). Сombat log looks like: 570 (1000) for no crit. 0,95 * 0,6 * 1000 = 570 342 (1000) for crit. 0,95 * 0,6^2 * 1000 = 342 This means that only damage/crit resistance from tenacity works.
Still not working. Tested it with a sword of "Avatar of War" set, which has a constant (1187-1187) damage. Without buff Sure Strike deals 877 + 96 = 973 (at-will tooltip is correct). With buff Sure Strike deals 880 + 96 = 976 (at-will tooltip is wrong) Аlso 96 does not look like a 18% of weapon…