About fire 2?

[Seraphor]

If you compare it directly to only Flare, then sure. But compare it to the dps of the entire rotation

It's been done.
Past level 68, Fire II is a DPS loss.
Before level 50, Freeze Spam is the most effective AoE rotation.

Following figures all based on 3 enemies. (adding more enemies makes the gap in dps bigger)

Freeze > Fire III > Fire II > Flare > Flare (transpose) [repeat] equals 2616 potency over approx. 15s or 174.4/s
Freeze > Fire III > Flare > Flare (transpose) [repeat] equals 2256 potency over 12s or 188/s
More Flares via Manafont/Ethers just bumps those numbers up but the gap is still in favour of no Fire II.

If you do your 2x Fire II rotation.... it's even worse.
Freeze > Fire III > Fire II > Fire II > Flare > Flare (transpose) [repeat]
That's 2976 over 18s, or 165.3/s

That's without any instant casts.

If you swift one of the Flares, then it becomes 12s and 9s respectively, for a difference of 218/s with Fire II v 250/s without.
Triplecast three Flares with Manafont, and it becomes a difference of 347/s with Fire II and 444/s over 7s without it.

Only case where it almost evens out is if you Triplecast a single Fire II plus 2x Flare, then it's 373/s with Fire II, and 376/s without. But that's mainly because without the Fire II you're wasting a Triplecast proc.
Your 2x Fire II this way works out to 297.6/s, and if you Swift + Triple cast for all four instants, that's 372/s for your best possible output.

So yeah, Fire II is a flat DPS loss.