WARNING: The following article contains spoilers for Cable #9 by Gerry Duggan, Phil Noto, VC's Joe Sabino, and Tom Muller, on sale now.
There's a reason Magik was chosen to be one of Krakoa's four Great Captains of Krakoa. Illyana Rasputin is both a powerful mutant and an experienced leader. However, her most notable achievements in power and leadership don't stem from her time in the X-Men; they come from her long-held mantle as the ruler of Limbo, a hellish dimension filled with demons who give her the royal treatment.
And when Cable went to Magik for help in tracking down his evil counterpart in Cable #9, Stryfe, she took him on a trip to Limbo to look for way to track him down. But their brief sojourn into Illyana's Llimbo reinforced why she is so respected and well-suited for her role in leading part of Krakoa's military efforts.
Upon arriving in Limbo, the demons inhabiting the dark dimension showed Magik the utmost deference. They gave her what she wanted without question, a moment alone with N'Astirh, a demon who has been a persistent thorn in Illyana's side, now her prisoner and being tortured as punishment for his various crimes.
Of course, it also doesn't hurt that Magik has reconstituted Limbo all by herself, so the demons probably owe her some deference. But as she's demonstrated, she is not afraid to punish those who defy her. So while gratitude for what she did may be a factor, fear of her authority and power certainly play a big role in her dominance as well.
But the fact that Magik was so well received in Limbo is a testament to her skills as a leader. She referred to herself as "the landlord, the cop and the Beyonce of this place" So she is equal parts leader, enforcer and celebrity of the dimension. She has authority, but Magik has managed something that few leaders can successfully achieve: she has found the perfect balance between fear and respect that keeps her subjects in line. Considering what she has done with actual demons, handling mutants shouldn't be much of a problem for her.
This sheds more light on why Magik was named as one of the four Great Captains of Krakoa. The roles were created by Krakoa's leadership, the Quiet Council, to lead Krakoa in matters of defense of the state or incursions for the nation's interests. Each captain is given their own jurisdiction to divide up the work under the command of the Captain Commander, Cyclops. Magik was placed in charge of managing the younger squadrons of new mutants. This task is essential to Krakoa's future, and its one that requires a hand capable of instilling respect and trust in the next generation.
Magik has this in spades. She has a perfect understanding of the line between discipline and abuse and is not afraid to teach hard lessons to prepare the future of mutantkind. The simple truth is, this particular job required someone capable of having compassion but not letting it get in the way of effective training. The children Magik has been entrusted to teach will be throwing themselves into danger one day.
Whoever has the job of teaching the next generation must have a certain ruthless streak to them, but temper it with enough wisdom to know where the line is between a teachable moment and punishment. And considering the amazing work that Magik has done with bringing Limbo under her control, teaching a few mutant kids shouldn't be too hard for her.