design complexity has crept up and the original legendary birds, as beautiful and mysterious as they seemed at the time, wouldn't look out of place as the end of a standard regional shitbird line now. conversely there's plenty of non-legend modern pokemon that look more powerful and mythical than the legendary roster back then.
you're tasked with going back in time and convincing the pokemania generation that a standard pokemon is a secret hidden legendary. which ones do you think would fit the bill? bullshit some pokegod style lore if you feel like it.