It really depends on the fight. Garuda, for example, depending on the group's DPS, if you can squeeze out the 2nd flare before she jumps, then you transpose, get to full while she is doing shriek, start over when she gets back. Even on a fight where the target is available full-time for DPS it's not a bad way to go. You at worst wait for one full tick on your umbral and you can start reapplying your thunder with that much MP then follow that with an ice spell, cap out your MP, and go back to fire, because fire is where your damage is.
Flare, Convert, Fire, Flare (or Flare, Convert, Fire, Thunder II/III, Flare) is great burst but not necessarily optimal sustained. I think I also get around 1100 or 1200 on convert, but I don't remember exactly and I logged out on MNK last night so I can't check my BLM's stats atm.
We can nitpick optimal skill use order all day but theorcrafting stats to fall apart when you're having to dodge, your buffs are timing out, bosses do things to interrupt your casting and/or rhythm, etc. Adapting the general purpose smart approach to the situation will get the job done.