Spells that don't exist that should

[Losie]

We've all been talking about Bardark and Barlight, which should exist, but there are a few others that should exist, but don't.

Light seems to be more common, for some reason

Banish -> Dark
Banish II -> Dark II
Banish III -> Dark III
Banishga -> Darkga
(You get the idea.)

Holy -> Unholy?

Diaga -> Bioga

What exactly was the reason in this imbalance between Light and Dark?

Barslow. Bardark Barlight would be nice too, speaking as RUN.