Just a small thing to add since MP cost is bring brought up a lot. Almost all the healing spells in the AST kit has a cheaper MP cost versus their equivalent. This MP cost reduction is usually 10% outside of a few exceptions. Benefic is actually 20% cheaper and Aspected Benefic is actually more expensive when compared to Regen in Diurnal (and much cheaper than Adlo when compared to Nocturnal).

The only outlier in the DPS skill tree that is present is Gravity for reasons stated above.

I feel the reason this happened initially was stated earlier - AST spells were generally 5% less potent at its launch and the mp cost reduction was to help balance that. Lower potency isn't the case any longer though.