Honestly, most fights don't last long enough for the extra debuff duration to make that much of a difference imo
Exactly. Most fights in the game are so trivialized by level 9 PC that the enemies just explode into paste regardless of what you're doing. The few fights that
aren't are generally characterized by a boss that gets 3+ actions for every one of yours. This means you get full advantage of your DoTs, which tick on their action, not yours. Likewise, these are the same fights that actually have the potential to punish a strategy that revolves around spending multiple actions setting up with debuffs and non-stance at-wills.
Ironically enough, the best enablers for "charging my laser" nuke strategies are a 6-action Abjure or Unbreakable depending on the fight, of which Black Mage has access to neither.