nooooo! cough cough! ahem! 
ok, class, please look at the screen and take notes. 
Crushing Blow & Crit Damage work differently, although they are calculated at the same time. (the chance for Crit and/or CB is done at the same time)
CB has a % chance take 25% of your enemies Current Health. the higher the rarity of the monster, the lower the % of Current Health that is taken.
I haven’t heard of anyone one hit killing a monster of any kind on higher floors without using a Crushing Flames and/or Frozen Build. eventually, on higher floors, monsters have so much Health, it’s more about crazy high DPS or Chained High Damage (like a Poison Build or a Bleed Build), than just a one hit kill.
Critical Damage is a kind of Spike damage, and anything that causes damage can cause a Critical Hit, except for Crushing Blow or Crushing Flames.
Epiphany (5), Rage (5), +225% Crystal Crit DMG, +75% Critical Hit, +70%, or better, Deadly Strike, Brutal Mythic will get you about 50% of your attacks being Deadly Strike for 3x Crit Damage.
for normal builds, a Max Crit damage with Brutal is 15x of damage done on Deadly Strike. with Epiphany, you would get up to about 17.6x damage done on Deadly Strike with Brutal.
hope this helps, even though I wrote a lot.