>>11807521
>It was originally a poison type Evee
That has more to do with why it's a Dark type. It being nocturnal was a means to justify that.
The original Gen 2 Eevee trio was going to be Psychic, Grass, and Poison. With Psychic beating Poison, Poison beating Grass, and Grass being the Flareon of the group (weak to one, neutral to the other). It's possible Leafy was going to have high Special Defense to account for this, but all three only had placeholder stat values so it's impossible to say. Once Leafy was dropped, Umbreon swapped to the new Dark type to counter Espeon's obvious advantage, and stats were balanced to make them fairly evenly matched.

Regardless, I like the flexibility. Something shouldn't have to be the embodiment of evil to justify being Dark type.