In a single-player game, no one else is affected if you decide to stubbornly wipe 10 times instead of looking up a video or strategy guide. Social environments, and coordinating time constraints among multiple individuals, bring a completely different set of considerations.

If you're concerned about 'spoiling' brand-new fights:
  • Require the feature to be unlocked per-player, per-fight, by first clearing the fight at least once. (ie, a player can't initiate Flashcards unless that player has already cleared the fight once)
  • Or unlock the feature on a per-fight basis only once the content becomes outdated ('next patch' system).
  • Or allow each individual to opt-out of the display (similar to refusing to participate in a Ready Check). "Jophia Krownlege has initiated Flashcards for Akh Afah Amphitheatre (Extreme). View them? Yes | No"
  • Or don't join parties that want everyone to know what's going on before pulling.
I don't understand how a Flashcard system is practically any different — or worse — than "Watch a video", or having 4-5 sentences of explanations typed out before the pull. Similar to how the in-game Countdown feature is just a streamlined improvement over the historical macro hack.