On crushing blow normal without crushing flames:
25% on normal enemies.
6.25% on magic enemies. (25%^2)
1.5625% on rare enemies. (25%^3)
Epic enemies is 0.390625%. (25%^4)
Legend enemies is 0.09765625% crushing blow. (25%^5)
Mythic enemies is : 0.0244140625% crushing blow. (25%^6)
This is without crushing flames (5). The crushing blow formula is that for every higher rarity, you do 0.25×0.25 . This means 25%×25% . If you square 25% , it is halved. If you cube 25%, it is halved again. Basically at epic enemies 25^4, legend enemies 25%^5 and 25%^6 on mythic enemies.
At least that's what the formula was suggesting before the codex changed the writing but it should be true.
With crushing flames. If you have crushing flames (5) , you increase crushing blow by 250% on Immolate or 25%×(1+250%)= 87.5% crushing blow or something along the lines. I mean normal enemies do appear with no visible HP when crushing blow and crushing flames takes place.
Crushing blow + Crushing flames (5) :
On normal enemies: 87.5% Crushing Blow on crushing flames.
Magic enemies: 87.5%^2 = 76.5625% Crushing blow.
Rare enemies: 87.5%^3= 66.9921875 % crushing blow
Epic enemies: 87.5%^4 = 58.6181640625% crushing blow.
Legend enemies: 87.5%^5= 51.2908935547% crushing blow.
Mythic enemies: 87.5%^6= 44.8795318604% crushing blow.
I could of course be wrong and it ends up as 62.5% crushing blow instead.
In which case. Crushing flames (5)+ crushing blow if calculation was different aka 25%×250% instead of 25%×(1+250%) .
Normal enemies: 62.5%
Magic enemies: 62.5%^2= 39.0625% crushing blow.
Rare enemies: 62.5%^3= 24.4140625% crushing blow
Epic enemies: 62.5%^4= 15.2587890625% crushing blow.
Legend enemies: 62.5%^5= 9.5367431641% crushing blow
Mythic enemies: 62.5%^6= 5.9604644775% crushing blow.
Even then, crushing flames is so powerful that it's basically a must have in high floor climbing. The damage Increase it's just too good for people. One problem however is that if enemies are immune to Elemental Crits such as Fire such as in some mythic enemies, that benefit gets nullified . Maybe even so in legend enemies too.
But combining crushing flames with things like Frozen turn out very well, plagued and other combinations. Weaken of course helps on the actual damage (not the crushing blow).