But after mb ->mm(1.3s) -> fb1(1.3s) -> mm(1.3s) magic blast has cooled, and fb1 -> mm(1.3s) -> mb(2.3s) -> mm(1.3s), firebolt has also cooled, so it's still continuous that way without cooldown empowerments. (I think) (The time listed is how long each spell took to discharge when I timed it previously)
Granted I have a very low opinion of magic blast so that might just be it, I try and avoid using the thing like the plague due to that discharge time which never did significant damage for me even with a 5 damage empowerment to be worth the 2.3 seconds compared to magic missile 1's damage / 1.3 seconds
And yeah, I have 15 second cooldown spells in use, but I have other things that I'm throwing during that so it's still constant fire over the 15 seconds, although the second half of it is slightly clumsier than the first half
(But I do like mage discussion!)