Relative power scale of spells?

[Cilia]

It's probably dependent on the individual's power level. It's extremely uncommon to see something beyond the basic "Holy," since it's typically the offensive White Magic. The name variations are more than likely there as the spells are all variations on the basic "Holy."

Alexander Prime's Mega Holy is probably the most powerful, relatively speaking. He is the soul of a sentient magitek steam colossus... who can manipulate time... and use holy magic on top of all that...