There is a flaw in Kaito's logic. When he was talking about how as people get stronger, they lose compassion, he was thinking about Yggdrasil, but he considers Yggdrasil weak.
I think Kaito's speeches in this last episode were written in a rather odd way. He obviously values personal power, but dislikes the power of faceless entities like corporations. Yet, in this episode, in different scenes he expressed his opposite views about the two kinds of power, while using the same terms for both of them and without directly comparing them to each other.
In his speech to Mai, he talks about personal strength and weakness, and making a world for the strong. Meanwhile, when he gives his speech to Kouta, he talks and criticizes the powerful collective, like Yggdrazil. However, he talks about both of them in different scenes just using the same terms about power and strength, even though they aren't really the same, and also never contrasts both uses of the terms directly.
Malika didn't even really support most of them. I can't think of anything significant she ever did that was truly "her." Malika's role as "support" is more akin to putting a plank underneath a perfectly stable table. Yes, the plank will technically be more supported, but it'll be fine without it there too.
Well, Kaito got a Genesis Driver and was allowed to continue working alongside Ryoma's group due to her, since Ryoma had lost interest in him after his defeat to Demushu. She also saved Kaito's life there. Earlier on, she was pushing Micchy towards dirtying his hands. In the overlord arc she accomplishes very little, but that's just due to her being a supporting player to Kaito, who also fails to accomplish anything relevant there and was mostly support himself.
Mayu, meanwhile, may not have transformed much, but she was still fairly important comparatively to the story.
Mayu failed in her quest, failed to help the villain, due to Wizard recovering Infinity when it was necessary, and failed to redeem herself in the end due to being too weak. It's not only the lack of transformations. She has very little value to Wizard's narrative. Ending the series alive doesn't suddenly mean that she was a well handled character.