Vect is going to do his best work hitting any independent characters in the army. The best way to run him is to team him up with a squad of Wyches and a cheap Succubus with an Agonizer. Overwhelm your opponent in power weapon wounds, IGNORE Draigo himself and focus on killing or tarpitting the rest of the Paladins. Only put models in contact with Draigo if they can prevent him from getting to your Agonizers/Vect
However, this is not the optimum method for killing Paladins. The best way to achieve that is to kill units in shooting with massed Darklight spam. Every turn, put as many darklight weapons into a single Paladin squad as you can, then put poison into it afterwards. If you can do this to a squad that ISN'T Draigo's all the better--his 3++ and EW are going to make even your Ravagers blink. Speaking of Ravagers, this is an excellent time to give them Disintegrators. 27 Ap2 shots each turn? Yes, please!