If the party has uncommonly awful dps, double flare rotation does have it's uses, but Fire II still has it's place even then.

As a BLM almost everything is situational, fixed rotation's regardless are not a DPS gain.

More often than not, it's actually better to (Transpose - Fire III - Flare) than to use the double flare rotation anyway.

A BLM friend was using the flare only rotation, he got another friend (healer) to parse while we did a few Bray, both as BLM and equipped the same i90 gears and weap.

Apparently his dps was at least 100 less for the full duration of the DG.

He now uses some Fire II and his DPS is a lot closer.