As I was interested in starting Fire Burst I thought I'd write up what changed using the character of u/killeen22's recent post as reference.

First I'll give a quick overview over what's changed

Skill changes:

• base damage was nerfed by about 26%
• damage effectiveness was nerfed by about 26% (I will be adjusting Immolate to compensate)
• cooldown is only relevant for clearspeed (especially after the blowback nerfs)

Cluster changes:

• shock from cold conduction is dead. (-23%)
• burning bright is close to useless (-5% total dps each) *3
• blowback is heavily nerfed (-5% total dps each) *3

Support changes:

• ignite prolif, unbound ailments, burning damage and deadly ailments can pretty closely compared to gem lvl 1 now and swift affliction lvl 7 (-50%)
• immolate loses about 3-4 levels because of the damage effectiveness, so I'll calc with a lvl 17 one (-14%)

Ascendancy:

• if you didn't go golems as elementalist nothing changed

Calculations:

Just combining the numbers we get:

0.74 * 0.77 * 0.85 * 0.85 * 0.5 * 0.86 = 0.177

So roughly a 82% damage nerf and a cdr nerf for clear as well.

I threw together an adjusted PoB to visualise this: https://pastebin.com/b9YCn5pD

Conclusions:

• Fire Burst was hit pretty brutal, I haven't played it before but 400k with very good gear seems rough.
• That said I haven't looked into alternative passive tree / cluster options, so maybe there are better options now (this is especially true for the cold conduction cluster)
• Maybe staff is better for better dot multi values now that there is less on clusters