I always see these "My dps on T8 is x, shouldn't it be y"? I'm a bis 110 BLM and my DPS on T8 can sometimes be as high as 470ish (maybe more? Idk I stopped checking a while back since there wasn't really a point anymore with it on farm) and sometimes as low as just over 400ish. This isn't because I'm dying, or because I have tower duties. Its because of 2 major reasons, and they are the biggest things I always ask people who posts these threads:
A. RNG bud, we're Black Mages we live n die by our procs much of the time.
B. And this is the big one: How much is your Bard using Foes Req.
Every once in a while you'll see a guy yell out "OH YEA I DEW 550 DPS ON T8 AS ILVL 92 BLACK MAGE LAWLZ" and you gotta keep in mind that if the Bard has foes req up literally as much as possible (which in a geared T8 party with healers who won't need mana song and Monks/Dragoons/Bards that know how to manage their TP shouldn't be hard) then your damage will be high. If its up for only the first 30 seconds of the fight it'll be much lower. Sometimes our Bard runs it multiple times through the fight, sometimes our Monks complain 10 seconds into the fight about their TP. With Laev even at ilvl 109 if you're doing anything around 360-400 that "makes sense" for a typical BLM. As people noted, yes timing raging with your swift flares are important and do that. But keep in mind your mechanics: Weave thunderclouds for firestarter procs, if you're near the end of a mana dump with a thundercloud proc, go into blizzard THEN use the proc for best uptime on damage, transpose fire III if you have a proc in blizzard, etc. You'll do fine.
EDIT: Oh yea food. If you're accuracy capped your using the right food then with Black Truffle, which with a Leav shouldn't be that hard (SO MUCH ACCURACY ON DAT THING THO). In BiS you'll be around 461ish accuracy and using Omelettes to make up the last bit of accuracy. Though with the recent findings in Black Mage stat weights that could be outdated by now, but their still is a lot of discussion going on with that, so I say just stick with the current thinking.