A permanent Foe's Requiem attached to Thunder would be too strong if it applied to all magic sources, particularly SMN. If it only applied to BLM damage and didn't stack with other Thunders, that'd be something to consider.

I think BLM would be perfect if it just reverted to the 5-10% stronger DPS 2.0 BLM had from a much looser UI3 phase and the free Firestarter check from the first Fire after Fire III. The only reason SE nerfed the UI3 > AH3 qualities was to rectify double Flare rotations, but they should have just directly solved the issue without a nerf, IE given Flare an independent recast of 10 seconds or so regardless of GCD recast, resettable only by Convert/MP Potion so as to allow intended double/triple Flares.