Are you talking about deranking the frostball? If this is the case, the scaling of magic damage for spells is (time cast)] / 3.5. A frostball with 2sec cast (reduced to 1.5 with talents) there will be 57.1% of the spellpower actually converted into magical damage. While with the max rank frostball with 3sec (2.5 with talent) the scalling is 85.7%
Why do most frost mages not spec into having the 1.5s cast time on frostbolt if that’s the only spell you need to cast in MC/BWL?
Not sure what you mean - here I am spec'd frost with Improved Frostbolt which reduces cast time from 3 seconds to 2.5 seconds.
Are you talking about deranking the frostball?
If this is the case, the scaling of magic damage for spells is (time cast)] / 3.5.
A frostball with 2sec cast (reduced to 1.5 with talents) there will be 57.1% of the spellpower actually converted into magical damage. While with the max rank frostball with 3sec (2.5 with talent) the scalling is 85.7%