On the point of BS spam, I will say this: I can't get hyped for that kind of "you can do X ability Y number of times in a row! WOWE ZOWIE!" thing anymore... and I feel like it may have to do at least in part with the animation.

For me, warrior more or less gets a way with it cause Fell Cleave's animation is just really good. It has good momentum and you "feel" the sort of resistance your axe meets as you... well, cleave the target. Dark knight's BS animation doesn't do it for me for some reason. You spin your greatsword and slam it on the ground, lifting your body a bit to convey just how hard the attack is... and then there's some kinda darkness beam thing. Y'know, maybe it's the lazor itself. Fell Cleave's graphical effects assist in conveying the sensation that you're cleaving hard whereas Bloodspiller's beam is... just a beam.
While I do get your point on the animation, I am pretty sure I wouldn't care about the animation if Delirium caused some auto dcrits (or even just crits tbh) like IR does. It doesn't pack the same punch as Fell Cleave spam both in animation and in actual effect on the target.