hm i feel like the distinction comes down to vibes here. if i were to be reductive i could describe the One Ring in a similar way “it corrupts gollum, gives Frodo a quest, makes Boromir crave power and turn on his companions in a moment of weakness, and (from Sauron’s POV) hobbits destroying it is a deus ex machina”. imo horcruxes as an idea were not that bad but,

to me, the main difference here is how they’re used in the story. The One Ring is the driving force from the beginning, it’s already well established in the lore of the world, and the only surprise to the universe’s scholars is how it suddenly found itself in a hobbit’s hands. Where horcruxes appear suddenly in the second to last book (obviously not counting the diary because it’s clearly been deemed a horcrux when JKR came up with them and thought the diary fit the vibe well enough). First 4 Harry Potter books are bascially episodic, an overaching plot only emerges by the end of book 4. And LOTR is one cohesive story with a clear goal from the beginning, which allows it to unravel in a satisfying and effective way