The mages aren't useless. The heart companions and elephants are ok units, but what you really need is magical units.
Mystics are the most versatile elemental mages in the game--they can pop with anywhere from 1-3 books of any given element. Priestesses are cheap upkeep and are good for research/healing. Both of these units can be hired at any fortress (recommend a cheap castle). Astrologers can cast Acaschic Record out of the box and some can spawn with Astral 4.
I don't put too much stock in the units, you need money (order) and maybe research (magic).
Hire lots of mystics and look for these guys:
1 Any mystic that can cast a nice evocation (magma bolts/eruption, Gifts of Heaven (rare), etc.).
2 Any 3 book x 1 element mystic--makes booster items.
3 Any 1 book x 3 element mystic--good site searcher.
4 A 2 water mystic--clammer.
There are incredible possibilities with Arco-Default. A pretender with 4-6 Astral can (with relative degrees of ease) be set up to do Wishing/Arcane Nexus, 2-4 Nature will get you a way in to the Ivy Kings and hordes of Vine Ogres. Try the Daughter of the Land for some early clams, an Enchantress for a little Astral boost, a rainbow mage for some versatility, or you could always go with the SC Nataraja--you don't have to worry about battle wounds or god recalls with all those priestesses hanging around. I like to take Death magic for Revenant/Spectre (researchers), Wraith Lords, and the Tartarian Gate (priestesses cannot heal the undead, unfortunately).
Golden Era is good too, Philosophers with Magic-3 will give you insane research and they're incredibly cheap (capital only though
) Plus, you get to keep your mystics.
Arcoscephale = Magical Versatility + Excellent Research