@hypolite Out of 5 bands mentioned only 2 are actually idols and none of them ever replaced an older member with a younger one.
The song "Nerve" (among other) is being sung by Bish and specifically address issues with the Japanese idol culture with the intend of denouncing it.
Two of the bands you mentioned started from very controlling agency and had to fight to gain their musical independence and are proud to have done so.
3 of the bands mentioned started with kids members that are now adults. There is not a single incident reported. No drug, no sextape no nothing...
This being said. Junior idols exists, gravure idols exists, the story of Rei Kuromiya is real but... Am I posting and encouraging this in any way?
Also, Idols are popular among teen too!. Both kids, teens and adults are welcome in the idol world!