I'd like to argue Ilyana above Boyd and Oscar, below Edward.
Thunder will be just as inacurate as axes and Greatlances, She'd be better for a Bolting, but gets her own SS weapon, Boyd gets you a Spirit Powder, but you have to draft Mist as well for that, and Mist is, well....Mist.
Her compatition for an early mage is Soren, since Micaiah is healing, and Tormod is never around. Calill is stuck in Crimea, so there's that as well.
Boyd has Jill, Nolan, Haar, and Titania. 4 competators, compared to 1. And Boyd's 2-range options are Hand axes, which break quickly and suck at hit, or Bowguns which suck at damage. Ilyana's options are everything, which suck at hit, but she's going to be ranging a lot more, but doing more damage compared to his options. She also gets inate Shade, while if you want a skill for Boyd, you're gonna have to transfer it over with Ilyana or Brom or someone, or take one off of someone.
She gets 8 chapters over him, and in Normal mode, should only be around 4 levels below him, depending on who else you draft, and when you promote her. Her mastery skill will also help get rid of all the magic bosses in the tower, but I suppose Boyd's helps since they don't have great defense.