Let's discuss Iris Havengard

Assuming spells of power 60-100, one way to increase the power in a vacuum would be to perhaps exploit the effect of MP-fueled critical hits, which will cause spells that do not ignore defense to hit for twice the damage, so long as the wielder still has MP to critically hit with. To facilitate this, you could even start her off with a Rune Edge as her initial weapon. Depending on the scope of the project, as far as other changes being made to make it so that Iris is not being placed into the game in a vacuum, other such pointy-stick class weapons such as the Crystal or the Falchion could also be made to use MP to critically strike, in an attempt to keep the physical portion of her damage relevant throughout the game(especially considering that the Rune Edge in vanilla has a pretty poor Battle Power stat).

As an aside, Blizzard sucks. Storm, being effectively identical to the elemental skeans in all areas except element(they all have 100 Spell Power), would be a better pick here. Bio Blast(the Magitek skill) would perhaps be fitting for Poison element. It's significantly weaker than the Power 100 skills, but comes with a couple status ailments for the sake of utility. For Earth, perhaps consider Magnitude8, which is also a Power 100 skill. Short of buffing Scar Beam and removing it from early game enemies that use it, there's no suitable equivalent for Holy-elemental damage, however. Alexandr, in terms of stats alone, is close, but it's more powerful than the rest, which is not great, and it's not thematic at all.