Galarian Zapdos is not a bulky attacker, its a fast, frail, powerful physical attacker with weaknesses to some of the most common attacks in the game, like Ice Beam, Moonblast, Thunderbolt, and Psychic. You could've chosen any item for a fast frail attacker, but you chose King's Rock? You're putting your all your hopes of winning into a terrible item with only a 10% chance to activate. Base 100 Speed was super fast generations ago, now there's Sand Rush Excadrill and Pheromosa running around everywhere. Max 328 is slower than Garchomp, which isn't exactly speedy by OU standards. Flinches only happen when you outspeed, which makes King's Rock an even more useless item