prosfilaes
Adventurer
To say that there can be no such person arguably confines the player character not just to a particular race, but also to being an ongoing protector of racial secrets lest they become such a reprobate.
Or elves just have the dexterity and magical control to do this, whereas a human, no matter how well trained, could never do it. The problem is that feels like it could be true in the LotR, but D&D (5) elves have a +2 to dexterity and can't be put to sleep, which just doesn't feel like they're different enough that they and only they could become bladesingers.