Yes, I was thinking that too but their speeds at improving are way to far apart, he's already garnered a good amount of people on his side that are 100x stronger than her. Even if he wanted to help her grow there are better ways than taking her into a place beyond her levels that could potentially kill her
The fact that he’s already saved her twice and now she’s stuck and unable to fight just proves your point. Also he can’t go all out while he’s around her. In the fight at the arena he literally soloed multiple higher grade fin demons but during this recent fight in like chapter 51 he purposely played as “bait” to the demon so that she could make a surprise attack. Which is cool if he wants her to get more experience and level up or whatnot but that’s just slowing down the plot of the story. When in other previous chapters they explained that he’s leveling up quickly on purpose to speed up the story so it makes this whole ark feel kind of pointless.
Still trying to find the purpose of her being there? Thinking logically his regeneration speed is already significantly good and she'd heavenly hinder him going all out in unescapable situations. Furthermore he can't continue protecting her everytime there is a sneak attack... and taking into the account that she isn't a special case like ang we can't deny her talent , yes but that's where it stops she is way to undeniablely weak in this current context.