DRK and DRG are extremely easy to counter in Frontlines

[FenyxRising]

BLM may do more damage in total, but in execution of the DRK combo, you'd want as much damage in as little time as possible (before people use Guard). In that, AST does way more damage than BLM can reasonably output in that timeframe. Flare + Superflare (15000) or Foul (16000) vs Doublecast Gravity + Macrocosmos (28000).

100% this

Only DRG comes close