To the GM.
And yeah thats quite possible to, like the way you think.
But either way it doesnt add 23% crit damage to the M/w damage while casted, thats certainly a difference that would be more than average, do the math on it. Flame on something for 100k then cast Intensity and Flame, Bet 5k diamonds it wont be 123k next time you crit.
You don't mean that bet

On lvl 5 mobs, without rings. I hit flame 4 times all crits for an average of 197k damage.
I then used Intensification(60) and casted flame 4 times, all crits for an average damage of 240k.
At level 60 i get 21% more crit + 2800 extra raw damage (though skill says magic damage)
That is more then 21%
Now i put my rings on. Castled flame 4 times for a average damage of 354.9k
I then used Intensification and casted flame 4 times for an average damage of 403k.
This is about a 14% increase in damage, however it really is adding 21%. The reasons it is not 21% is how the formula works.
The damage 21% is to your original damage. % do not stack just like how it works for speed buff.
When you use catalysis and spirit water you don't get -80 % casting time.
My rings each give 48% so its like speed buffs, you don't get 48% + 48% + 21% for a total of 117%.

i suck at explaining so sorry if you don't understand
the 354k damage had 21% if my original damage added to it, not 21% of the new damage after its been giving the rings extra damage.
that is why the amount the 354k damage went up was about the same number as the original. around 43kish