In short: It's Touma.
I ultimately cannot get behind everyone being inspired and changed solely by Touma as that crushes agency in a lot of characters, characters (especially females) should have their own motivations for becoming better people, if Touma is always at the center it feels like the Touma Show and like the world bends over to give him a sloppy toppy.
There are more reasons for why I detest Sprengel, Aradia and Aleister's character change but if there's a main reason it's ultimately that I'll always prefer Toaru as a story where characters have their own individual paths created by themselves and don't abandon their motivations because good boy Touma wanted them to fight for him.
This is why I don't like some Toaru females as they ultimately feel like complimentary pieces to the males, Hamazura and Accelerator tend to do this to the girls around them as well.
For a character like Alice that sort of development is fine and endearing even because a child being guided by an older figure that genuinely cares for them is completely natural, when the person is either a grown ass man like Aleister or a grown ass woman like Aradia and Sprengel then they're characters just aren't doing much of value.
I'd prefer Sprengel if she stayed a villain that perceived Touma as boring for his hero gimmick and already saw his spectacle when Jesus Christ was alive and the absolute closest I got to liking Aradia was when she made a flower for a sick child at a hospital because the moment had nothing to do with Touma. That was a return to form to the Aradia we saw in GT6 that wanted to protect people who were rejected from society like witches.
Sprengel's talk about looking for a King that will basically make her happy just reads like bad wish fulfilment, you're supposed to be your own person. That's called strength and its what Kamijou Touma does for himself.
Aleister's character was better off retired after Coronzon arc in my opinion as not only is his redemption just not a good idea on principle (4th hero rivals Naruto calling Obito a cool guy) but it being done through Touma is utterly painful to read through. This man Kamijou Touma is the center of the goddamn universe and a character like Aleister who once fought for himself now only does what Touma wants, that's just disheartening.
Kamijou Touma at his best is a very helpful figure that ultimately has people he can't reach like Terra and Acqua and characters like Acqua end up becoming better on their own through their own will. It's why I enjoyed Trismegistus in the Transcendent arc as he went through an arc of rejecting his Transcendent mentality all by himself and deciding to finally help Touma save Alice instead of falling head over heels for Touma and becoming a better person because of him.
Touma is awesome, I wouldn't make him my namesake if I didn't love him to death but he genuinely ruins a lot of characters that should be independent actors.
The most that Touma should effect people is how CRC was beaten by Touma in GT11, as he fell Anna Kingsford confessed to him that she loved his teachings, that even though they were false she based her entire life on them so he should too, living to serve someone is a good ideology, in that moment CRC was influenced by both Kingsford and Touma and it was a character that wasn't Touma that finally made him change his heart.
Likewise the warm moment between Aleister and Kingsford was actually quite nice in GT10. The way that characters who are redeemed should be acting is building a network of connections with people who uplift them together, not just Touma since one character shouldn't do so much, it becomes bothersome at that point.
Accelerator changed because of his growing family, Last Order, Yomikawa, Yoshikawa, Misaka Worst and Qliphah Puzzle 545, Hamazura changed because he finally found something to protect in these ITEM girls, they both started by learning from Kamijou Touma but eventually realized what it meant to be the main character of their own lives.
That's what GT Aleister, Sprengel and Aradia lack which is the main reason (apart from some other things) I will never like these characters.
