I have more suggestions to balance out the Magic-types.
Solution 1: Shield of Heaven should be another MD/DP buff, just like you said. At the same time, Elemental Shields should be exclusive to Soul Masters and function in the same way Light Shield/SoH do. That way, both Pure and Hybrid get two MD/DP buffs.
Solution 2: Summon Boulder should at least do the same damage Drip Bomb does. This won't be so crazy considering that right now, Earth only has two "useable" skills in the form of Earthquake and Cleaving Terra. Deadly Fen becoming an Earth counterpart of Scorching Earth is not a bad idea either.
Solution 3: I know you've said this before, but HOW ABOUT REMOVING AC FROM THE FORMULA OF RAZOR GALE AND THE BLESSINGS? Wind is already as supportive of an element as it can be, why not give it a powerful skill that's single target for a change? They already have Razor Gale, all they have to do is revamp it. Making it as strong as Incinerate won't be so bad, as long as it's not up par with Dragon Storm.
Solution 4: Fix Light Wave. Srsly. The skill could be fantastic if the AoE were fixed because it already deals higher damage than Radiant Strike. Also, move it to Priest. Hybrid Light Mages already get tons of AoEs, so it won't be unfair that they move this skill to Pure.