Original Post — Direct link

FirestormFirestorm now calls down a large meteor that impacts the targeted location, followed by a series of smaller impacts at set intervals over the storm's duration. The base power of the spell has been significantly raised, so you are now limited to three Firestorms at any given time (any new storms created will replace the oldest).

  • Now requires level 28 at gem level 1 (from 12). Please be aware that existing low level characters with Firestorm socketed may have that gear slot disabled until the Firestorm gem is removed.
  • Now has a mana cost of 13 at gem level 1, up to 25 at gem level 20.
  • Now has an added damage effectiveness of 50%.
  • Now deals 22 to 33 fire damage at gem level 1, up to 207 to 311 fire damage at gem level 20.
  • Now has a base duration of 1.4 seconds with one impact every 0.2 seconds.
  • The first impact now has 100% more area of effect and deals 150% more damage.

The Comparison :

Rough calculations, rounded to whole number sometimes, so accurate calculation would be different however the result will be close enough.

I am also assuming every single firestorm impact hits, which is quite unrealistic however except for the first impact, the new firestorm suffers from exactly the same issue of missing impacts, But i will try to talk through this on end of this post.

I will be assuming "damage per cast".

Flat Damage :

Old : 200 - 300

New : 207 - 311

Result : ~3.5% more flat damage for New

Damage Effectiveness :

Old : 45%

New : 50%

Result : ~ 10% more damage for New

Amount of hits :

Old : 20 hits, over 2 seconds (10 per second)

New : 7 hits, over 1.4 seconds (5 per second)

result : ~ 30% total less damage for new, from duration decreaseAND ~50% less damage for new, from less frequency

First Impact Factor :

Old : None

New : assuming the initial impact hits, counts as 2.5hit

result : 7 hits effectively functions as 8.5hits, ~20% more damage

Additional Scaling :

Old : Duration and cast speed are straight up scaling multipliers. 90% duration from passive and very very pessimistic assumption of 50% cast speed, functions as 185% more firestorm dps, fully ramped. As for "damage per cast"'s sake though, 90% more damage from duration.

New : limited to 3, needs minimal scaling for 0.75 cast speed to match 1.4 seconds duration, However, it practically doesn't seem to matter as 3 maximum is likely to always be maintained.

Conclusion :

New firestorm has 3.5% more damage from flat buff, 10% more damage effectiveness (doesn't necessarily mean 10% more damage, however will assume insanely high additional damage to favor the new firestorm), 30% less damage from duration nerf, and 50% less damage from less frequency.

Math : 1 * (1.035) * (1.1) * (0.5) * (0.7) = ~40% damage per cast compared to old firestorm, while practically being unable to scale from duration and cast speed, which very easily functions as 200% more damage multiplier at the bare minimum investment for firestorm, getting worse as real investment happens. (talk to spell echo and stuff).

Hitting the Initial impact only serves as 2.5 hits, giving it roughly 20% more damage (~50%)

New firestorm has at best 50% damage per cast in a case where player does not have ANY kind of cast speed and duration scaling, dropping to practically 27% damage (duration clusters) or worse per cast, and only gets significnatly worse due to firestorm being limited to 3.

about how many firestorms hit & how first impact affects damage comparison :

The actual damage per impact haven't really changed much, favoring the new firestorm by about ~14% per impact at most.

Assuming half of the impacts hit (and assuming first impact always hits), number of impact hits change to :

Old : 20 -> 10

New : 6+2.5 => 3+2.5 = 5.5 (*1.14 = 6.27)

Assuming quarter of the impacts hit :

Old : 20 -> 5

New : 6 + 2.5 => 1.5 + 2.5 = 4 (*1.14 = 4.56)

special guest : fireball

Firestorm : 259 damage, 8.5 impacts (2201), 50*8.5 = 425% added damage effectiveness when 8.5/8.5 impacts hit

Fireball : 1369 Damage, 240% added damage effectiveness, scales with cast speed

Tipping point for firestorm to do more damage than fireball per cast is when 56% or more impacts hit (and then remember fireball is an instant dps spell and can be scaled by cast speed)

TL:DR

at situation where New firestorm is probably the most favored, where only 1/4 of the impacts hit and first impact always hits, no duration and cast speed scaling whatsoever, the new firestorm still does only roughly 91% of old firestorm's damage , getting rapidly worse with more impacts hitting the mob (conc effect, wink), duration scaling, cast speed scaling, very easily down to 27% of old firestorm's damage, assuming very very poor investment of duration clusters and 50% cast speed, and then it still gets worse.

GGG, Buff firestorm, to me this makes absolutely no sense unless i'm missing something very important. Firestorm was already basically not-so-viable skill as a main skill, practically only being used by eye of innocence shinenigans.

External link →
about 4 years ago - /u/Rory_Rackham - Direct link

The reason comes down to the area of each impact being significantly larger, in a smaller area, so each enemy is hit significantly more often per impact than before. I’ll see if I can confirm the updated radius when I get the chance, but off the top of my head it’s hitting targets more than twice as often per impact, maybe even three times as often as before.