This is why (despite loving the team-up) I’ve always had a bit of an issue of Illyana apprenticing with Strange under Bendis. She has been very well-schooled in the arts arcane since Limbo, but she gets treated too easily as a novice at them.
Now, that doesn’t mean she knows as much magic as him--I’ve always liked to see the Sorcerer Supreme as someone who knows every kind of magic, or near enough (treating the title as a set of powers that can be handed to anyone is dumb; there, I said it, alternate future Sorcerer Supreme Tony fricking Stark, or for that matter Billy Kaplan who is awesome but uses his powers without much learning)--but Illyana is a specialist, probably the greatest, in the magics related to Limbo.
I’m not sure how long Stephen studied with the Ancient One for? Regardless, Illyana’s seven years of training (mystical with Belasco and Ororo, and physical with Kat) came with demons to punish her when she didn’t learn right or fast enough. Bet the Ancient Nice Guy didn’t have a S’ym.
And like Stephen wisely says, her development as a non-traumatized human lagged behind a bit.
From Uncanny X-Men #190-191 by Chris Claremont & John Romita Jr.