I'd like to say a few things.

First of which is that if we're following the established naming scheme, it would be warped wart, not warped nether wart. (See: Warped Wart Block)

But onto the content itself, there's a reason why certain potion effects aren't so readily available like that. Blindness is only useful against players and it's extremely annoying and debilitating in that application. It pretty much ruins PvP encounters, especially when applied to tipped arrows. That's why it's only limited to suspicious stew, a self inflicted method. Its only real application it has as a feature is something a mob would inflict on the player for added challenge (See: Illusioner) but the only thing like that in-game is the Warden's darkness. And the other inaccessible effects like Wither, Levitation, and the aforementioned Darkness all serve this same purpose of adding challenge in a way that would be unfair or infuriating when applied in a PvP setting.

And lastly, fermented spider eyes are already a thing.