My point was that Fire IV PPS is lower because it's a 3 seconds cast. Using Thundercloud when you have your dot at 18 secs is a DPS increase. It is the same as using Swift Flare Convert on an opener. Also, a proc by default allows you to be more mobile.
Swift Flare vs Fire IV
260/2.5 > 280/3
104 PPS > 93.33 PPS
Fire 3 Proc vs Fire IV
240/2.5 > 280/3
96 PPS > 93.33 PPS
So you are actually wrong by overestimating Fire IV. The same mistake that led me to the conclusion Sharpcast Fire 1 with my current Spell Speed is better than the 6 Fire IV opener I used to use all the time. I still use the 6 Fire IV opener on A3S and it's only because this opener has the advantage to be more mobile at the beginning with the Swiftcast.
If you have good Thundercloud management, you'll use 1 proc in your Astral Fire and 1 proc in your Umbral Ice but in certain situations, multiple procs is handy for movement.
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