I think it's all the variables at play that make it an interesting game vs just watching a cartoon with 7 other people. You know those games that have scripted cutscene type battles where you have to hit triangle within 5 seconds of it showing up or you lose, or you have to pound X over and over before the zombie gets close enough to bite your face off, and thats the only way that mini-sequence in the game is going to play out whether you get it right or get it wrone, die, and have to repeat it? This isn't that kind of game. Usually the healer is better positioned for a raise, but sometimes one is keeping themselves and the tank up while the other is frozen in ice, stone, dead or whatever. If a healer has to be raised in a party of 8, and I have a full set of dots already going and aethyrflow stacks at my disposal, the other healer prob needs their MP to solo heal mmonetarily, more than I do. The questions originally asked wasn't solely in the context of a full on nonstop DPS race from the latest coil.
Another example- when does it make sense for a Bard to use LB2 against a primal? Pretty much never. But for the first time in like a year that's exactly what I had to do as Bard that s week with both healers dead, the rest of the party on the very brink of death, too much boss HP for a caster/melee DPS to finish him off before we died, and LB3 being unattainable before we would have wiped. I brought the tanks and other surviving DPS's back long enough for us to finish the battle, and that wasn't how the fight was supposed to go, but it sure as hell felt great having a risky call like that pay off rather than failure.
So my suggestion is- swiftcast shadowflare when you can and feel comfortable doing so based on your assessment of the overall battle. If you sense that you might need to resummon, or a raise might be imminent, do what you think is best especially if you can back that decision up after battle with a logical reason for it. And hey if you try to swiftcast raise someone but someone else beat you to it, if your shadowflare is about to expire or already went down, just do a new one before swiftcast timer is up- that new raise status symbol is super handy.