This had been Naruto's plan for Neji's future from before they had even left Konoha.
Naruto had planned this future for Neji long ago. The only exception would have been if Neji had refused to defect from Konoha alongside him back then. But now Neji had become an indispensable aide, so Naruto naturally needed to do everything he could to find ways to strengthen him. The great war was fast approaching. Whether they were facing the Akatsuki or the Five Great Shinobi Villages, Naruto needed to strengthen himself and his companions as much as possible. Karin and Utakata had already reached the limits of their potential and growth. Karin in particular had always been regarded as a support specialist. Given her current strength and mastery of Sealing Jutsu, once she learned Sage Mode and they took down that Rabbit Goddess, she would be able to provide significant support on any battlefield whenever Naruto faced an opponent.
As for Yakumo, her specialty was genjutsu.
Her control over the five senses had grown so powerful that even Naruto, if he wasn't in Sage Mode or Nine-Tails Chakra Mode, could easily sink into the illusion she created—a world of illusions that felt utterly real. If he couldn't break free from it quickly, Yakumo could use the "reality" she created to erase him!
And Naruto was already like that.
As for ordinary "Kage Level" fighters, there was even less need to mention them.
In other words,
as long as she had the right circumstances and could create the right opening,
Yakumo could easily kill any "Kage Level powerhouse."
Among the Akatsuki members, Uchiha Itachi was hard to judge. There had never been a clash between the Mangekyō Sharingan and a genjutsu that controlled all five senses, so who knew how resistant either side would