I have been trying to complete this deed with my crusder. I already had 7 points in it from when I first started the game and hadn't learned to properly utilise all the skills.

I rebound my armour skill keybind from 4 to 8, to ensure I couldn't press it by accident. Since then I have completed 2 full assignments, each of 5 missions, plus a couple more missions. This Heroic Deed has not budged a single point. Please take a look at it.