If it were me, I'd stick with Shadow on the Archmage. The only spell you're loosing out on is Mindrazor (and you can still cast that on your Spears!), and the hexes are a really good boost to PG's lacklustre damage-dealing.
You probably could get away with loosing the Level 2, but if you keep him, I'd actually pick Heavens.
Thing is, a big block of PG is just so obvious a target for the kind of nuke spells that don't allow saves (even MR) that he BotWD does start to look pretty essential, even if it does mean missing out on Mindrazor.
And I assumed that the Magi would be bunkered with the Archers. Can't imagine why else you'd be fielding archers. So long as you are though, there's no earthly reason to but Magi in a frontline combat regiment.
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