Harry's characterisation as the Kid Hero is torn to shreds by showcasing just how heavy a burden that role has become for him by the sequel. The neverending threats targeting him because of who he is/could be, start taking a serious toll on his psyche along with the mental trauma already built up from his previous adventures, to the point where he develops a serious case of Post-Traumatic Stress Disorder.
Carol is similarly afflicted, albeit to a significantly lesser extent, and both (Harry particularly) are used as examples of why the Kid Hero concept is a terrible idea. Harry in particular uses it as a reason to keep Ron and Hermione out of things as much as possible and to avoid Clark for most of the book, until Strange forces his hand, because he doesn't want them undergoing the same kind of experiences and turning out like him.
Leading people around by the nose with hints, comments, and selectively revealed information designed to manipulate them into doing exactly what you want them to do, playing them like chess-pieces, is a great way to win the metaphorical chess match. It's also a great way to get people to resent you at best, hate you at worst, especially when 75% of the time you refuse to tell them why you're doing it (even if that's a necessary part). Playing the Long Game also means that your personal relationships suffer in the process; as Strange sadly admits, he was an excellent teacher for Wanda, but a poor Parental Substitute, the latter of which she badly needed. That and his absolute refusal to help her with her pregnancy with Hermione, by John Constantine, who she had come to absolutely distrust, leaving her utterly isolated but for Lily Potter, as well as his ban on her taking in Harry after his parents' death (she was his godmother and had the right), critically damaged their relationship. While he had good reason to do so - Harry wouldn't have survived her enemies, and neither would Hermione - she also had good reason to resent him, especially given what happened anyway with Harry and Sinister.
Sticking to The Plan come what may, only altering details in Xanatos Speed Chess to get it back on track, even if getting it exactly right is crucial to saving the universe, leaves others overly reliant on you, meaning that the moment you get caught off-guard they're massively blindsided - as is horrifically demonstrated in Forever Red. Almost as bad is Harry Dresden's discovery that Strange manipulated events to ensure his and Thomas' birth, setting their mother, Margaret LeFay, one of his former apprentices, on the necessary path on the grounds that he felt they'd be useful, leaving Dresden in a full-on existential crisis. Strange is aware of this (contributing to his considerable self-hatred), and considers his actions Necessarily Evil, setting up Gorakhnath as a philosophical opposite to prevent Harry copying him, and arranging matters so that the heroes can stand up on their own when he's gone.
Jean Grey is a minor deconstruction of the Go-Getter Girl, Cool Big Sis, and All-Loving Heroine. She is genuinely all those things and loves both Harry, her cousin, and Maddie, her long-lost twin sister unconditionally. However, the sheer pressure of having to juggle her academic and sporting responsibilities, her de facto role as Head Girl of the Xavier Institute (which gets a lot of traumatised younger students), her lessons in her vastly expanded Psychic Powers, and being a Cool Big Sis to Harry (who's horribly traumatised following Forever Red) and Maddie, who's even worse, with a literal lifetime of trauma that means that she can barely function normally. Add a relationship into the bargain, and it's inevitable that she finally cracks under the pressure in chapter 47. Carol, in milder but similar situation, remarks that she's only surprised it didn't happen sooner.
