I really don't think "groomer" has a useful place in analyzing this story (or most any story there's pretty much always better terms that don't have the disgusting political baggage that we could use).
Let me say first that I agree with the entirety of your post, and I'm not taking issue here with anything at all about your reading of the story, just riffing off what you've said.
I do think it's interesting what the "idol" trope (in stories and in real life) does to the concepts of adulthood generally and to "grooming" specifically.
Taking the second part first, being "groomed" (as a performer and a public figure) is both figuratively and literally what becoming an idol is all about--it's all singing and dance training, deportment lessons, etc., and if a manager isn't literally the person doing an idol's hair and makeup, they're in charge of the people who do it.
And the idol ethos is specifically about keeping the performers if not literally infantilized, then in a state of enforced perceived adolescence--sexy but not sexual, desirable in fantasy by everyone but supposedly never partnerable by anyone in real life. These are professionals generating considerable sums of money (although apparently much of the revenue goes to parents, agencies, managers, etc.) who are denied most visible signs of transitioning into adulthood like drinking, dating, etc.
And that's just the most neutral "default" idol mode, not the documented extreme career pressure, overwork, media exploitation, online bullying and rumor-mongering, etc. It's pretty easy to see why being-in-control-of-not-being-in-control could fit an idol character in a series like this one to a T.