At its most basic, the argument for Fallen Empires is that it would create a great influx of playable decks, that it was released in 1994, and that it is the last of the old school "stand-alone expansions" (it came before the block structure we've had since Ice Age/Homelands/Alliances)
It also means a deck like my old Marath, Will of the Wild deck, which was built around pinging Dinosaurs with the enrage keyword, could use Kaheera
Featuring the beloved Charmers and their familiars, the deck brings a magical aesthetic to duels while maintaining engaging gameplay
Attack!" When Kaiba activates that monster's Trigger Effect, he announces "I now negate your monster's effects!" When Kaiba activates that monster's Quick Effect, he announces "I return Solid Dragon to my deck to bring a new Blue-Eyes!" When Kaiba Summons "Dragon Spirit of White", a cut-in frame of Kaiba's face briefly appears, and he announces "Emerge, Dragon Spirit of White!" Most of the time when Kaiba attacks with that monster, he announces "Attack, Dragon Spirit of White!" When Kaiba activates either of that monster's effects, he announces "Dragon Spirit of White's effect activates!" When Kaiba Summons "XY-Dragon Cannon", a cut-in frame of Kaiba briefly appears, and he announces "X and Y
Have all 3 of each (3x Pika, 3x Drednaw, 3x Alcremie, 1x of each power level)