There’s definitely a debate about how much parents should oversee their child’s usage of technology and in what form, whether guidance should be through advisory discussions, active enforcement with software restrictions, or a combination of both. I do not want to speak for the validity of the research cited in the linked open letter.
On Android, it is possible to download a parental controls app. You have to sign your privacy away to a third-party service that you can’t really trust but it is possible. The locked-down sandboxed security model of iOS means an aftermarket app cannot get low-level enough to override app launches and stuff like that.
This means the onus is on Apple to provide functionality like allowing access to apps during specific time windows or keeping an activity log of open apps so parents can see what their child has been up to.
I think Apple should offer these features and leave it up to the discretion of individual families as to how they are used, if at all. The fact that iOS has a Restrictions feature already says to me that Apple does not hold a principled stance against parental controls, just the current offering in iOS is lacking.
I would expect that any parental guidance features introduced in a future iOS would make it abundantly clear when they are used. Apple would not let parents secretly spy on their kids. Apple already does explicit signposting for phones that are being managed by an enterprise deployment system which has the potential for administrators to track the device location and supervise usage. Enforced Parental Controls would get similar labels.