I am making a build mainly for dungeons and pve, I was wondering if dragon's pledge was a good skill to use. Does the increase in defense rate make much of a difference or should I spend the skill points on something? Please explain.

Def rate = chance to block knockdown (if You use <R> guard)
I think its useless... waste of SP. But hmm... its give 2k def rate... but working if You got below 30% LP... what DW got less than 70%? I still think its uselsess... 5 sp to max it... Better spend it in 350 Melee defense or 868 LP (Passives from Warrior skill tree)

its not that it stops KD, because it doesnt, resistance does this.
Block rate is the chance u block an attack, also work for KD, but this thing makes u block attacks (When u see a blue icon above the player indicating that he blocked this attack) makes the damage 50% less, however, i used this only once but seeing that u dont need it in dungeons because if ur health is lower than 30% u will die instantly if u get critted, and ur health will always be over 80%
So i'd say u might wanna get it for TMQs only