This is also in base GD as far as I know, check out this post Advanced Mechanics
So in short, you miss 40% of your attacks. If you do hit, you deal about 15% less damage and you cannot crit. You have no crushing blow to speed up a fight significantly. You have no conviction (which adds a lot more damage through the resist reduction). The build you linked does crit, a lot, so probably has a 3x crit multiplier as well, and has mythical griswolds which does add a projectile i think to BH (so doubled damage that doesnt show on sheet).
It takes so long as your stats arent optimal as I’ve mentioned before. CB let’s you “cheat” a bit on the length of the fight, which is exactly what people use/need when they’re not fully endgame gear equipped. Once you are, you also no longer need CB.
Oh, and SR will be removed completely but that’s known already.