Have you seen a game where there is a all powerful artifact but can only be obtained by defeating the most powerful hidden boss . It is powerful but someone who could defeat the said boss that(the item) is useless. Especially since hidden bosses usually only appear after the main story.
In Ys, The Ark of Napishtim you receive a great item as a reward for defeating the secret boss, but the item is useless for the rest of the game because the player is so overleveled / skilled that the reward item is redundant. It's still a great game.
Final Fantasy Excalipoor I fucking hate that secret boss so much but absolutely destroying every single enemy and the final boss afterwards like an adult fighting an infant was pretty satisfying.
Any standard full recovery items in jrpg, their rarity made me reluctant to use them, all the way until the game ended
no specific examples come to my mind but, in general, yes. surprisingly often. either that or it's an item obtained early on but cant be used yet and by the time it's usable i already had gained even better stuff.
Endboss drops? Iirc in Fallout series (one or two I forgot), once you beat the game you are rewarded with godmode. In early Final Fantasy or generic JRPG games, the endboss drops a legendary weapon that does the same thing. Which is stupid imho because there is no longer any after endgame play value. Ps. OP is referring to key items rendered moot as players find alternative methods to beat the game.
Resident Evil 4 tommygun and rocket launcher(/w infinite ammo) are op and fun to use but the game is easy enough to not use it and it's more fun using knife to finish the game.
The fake Biggoron Sword in Zelda Ocarina of Time. It breaks after a couple of slashes or if you hit any object 3 times.
on release ? Diablo 3 you finished the story mode in 3 increasing difficulties reach lvl 50 and dropped your first set/unique for lvl 6 ... with a general trend to become the items you needed after you needed them so you were basically "naked" infront of every new challenge
Not really an item but a spell from FF Tactics called Zodiac It costs WAY too much MP for a spell so slow that your Summoner would be killed in a few turns before releasing it.