I believe Second Coil doesn't favor BLM because it's a tighter dps race in Turn 1 with average iLVL 95~ or so gear than most all previous content. As a result, you clearly feel the lower dps of BLM, whereas it wouldn't have been such a problem previous to this. If everyone's dps isn't top notch, you have to do more acrobatics to deal with mechanics, etc. BLM was around on par with MNK before they gave a flat increase to melee damage, so obviously when that happened MNK became clearly superior in any scenario where they could leverage their damage efficiently.
I don't believe MNK is overpowered in terms of single target damage. DRG is pretty much on par with them. BRD is only a bit behind. Depending on the specifics of the fight, SMN is either ahead of them, equal to them, or a little behind. BLM is clearly behind pretty much every other dps, by a wide enough margin to notice. I play with MNK, DRG, BRD, and SMN in my group, and everyone is pretty good. I personally play SMN/BLM/BRD, as needed, for whatever I do, and I basically only use BLM for myth speed runs, bc AoE, yo. If you're "clearly outparsing" everyone else with inferior gear as MNK, then everyone else is either a BLM, a BRD, or pretty horrible at their job (or your parser is broken, or a bad parser).
The main problems with BLM are 1) the PvP nerfs and 2) luck-based mechanics. It's kind of funny that even after nerfing Blizzard 2, BLM manages to face smash everyone on AoE, but the real annoying PvP nerf was halving the damage on Scathe, as well. Basically making your "on the move" damage pretty much garbage. Thanks, SE. Then, on top of that, whether or not you do even decent dps relies entirely on how many times you proc Firestarter and Thundercloud. If you're the luckiest person on earth, your BLM might seem competitive. More likely than not, however, you're going to be pretty awful. Unless every fight is like Garuda or Turn 4 and you need to clean up a ton of adds. But wouldn't it be kind of boring if every single fight was set up the same way? Hence BLM needs to not suck completely on single target, which is the present reality.
Personally, I would hope that they'd let you set up Firestarter and Thundercloud rather than luck into it, or completely rethink the single target rotation. Doing something like just making Fire an instant cast and calling it a day wouldn't work, because BLM has weaker damage on a single target even in the most optimal scenario.