(...)
Fire Nova - .214 coeff, min dmg 893
Lightning Shield - .33 coeff, min dmg 380
Flame shock - .214 for direct hit, .1 for dot, min dmg 500/834
Earth Shock - .385 coeff, min dmg 849
(...)
Now for Earth shock:
with similar min dmg, single cast deals more dmg than Fire Nova, but you can cast Fire Nova twice in the same period; when accounting for spell dmg -2k sp gives 1585 Fire Nova dmg and 2246 Earth Shock dmg with 5% dmg talent and 28% SS debuff. 528 dps vs 374 dps.
Even with T9 4p bonus and Reverberation talent, it only gives 495 dps for Earth shock.
Fire shock:
with 2k sp it gives, with 5% talent buff, 975 flat and 1085 dot dmg
Comparing it to Fire Nova, FS in 18 secs deals only 2060 dmg, while Fire Nova deals 1585 dmg every 3 secs.
Considering FS dps is only 114, that is the reason Fire Nova has higher prio and FS should only be cast or refreshed while Fire Nova is on cd/you are on the move.
Although it is also scaled with haste, haste cannot account for 5x dps increase.