you didn't read me...

the whole buff monk get lead to +75% of damage
+75% = +5% from fist of fire, +10% from twin snake, +30% from grease lightning and +30% from riddle of fire.

50 potency + 75% = 87.5 of potency. what is the weakest of all aoe the melee and the whole game have. generally the the basic aoe is 100 potency, what we don't reach even under riddle of fire.

why tornado kick is not viable while under riddle of fire it's mostly, because it consume our 3 gl stack that increase our speed of 15% and riddle of fire reduce the attack speed of 15%. in normal time riddle of fire under 3 gl stack put us into our...normal attack speed... not boosted. if you consume your gl stack for do a tornado kick... it will make you be -15% faster than normal. leading your attack speed around 2.6+ meaning you will loose dps... since after your tonardo kick not enough to be at -15% of attack speed you will be only at +45% of damage instead of +75%...

use tornado kick only for get a big number is the dumbest move ever... you don't get boost of damage from it since it will take you between 21-23 second (9 gcd) for get back to full stack if you don't have perfect balance behind, even with perfect balance you will loose 3 gcd for get back to full power.

that why tornado kick is considered like a niche skill, because it's utility it's when you can't save your stack... not used as a powerfull strike, since behind you will nerf yourself.
just an example of what i means:
our combo potency is the lowest of the game when not under gl stack.
our best combo is 140>180>170
with gl stack (+45% of damage we gonna count fist of fire and twin snake) 203> 261 > 246.5 (710.5)
with riddle of fire (+75% of damage) 240 > 315 > 297,5 (852.5)

if you go around you will notice that our combo are not the strongest around from far:
SAM => 140>280>400 (820)
DRG => 150>240>440 (830)
NIN => 150>220>340 (710)

the only saving grace of the monk (and if you did notice nin too) it's our fast attack speed, that why get +30% damage buff but a -15% attack speed is totally bad for the monk.