Just because you technically can access those endpoints, or at least used to be able to with a 3rd party client id, that is in no way an endorsement by Twitch that they ever intended for 3rd party apps to access those endpoints.
Saying that “Twitch clearly supports us using them” is nonsense, every statement by Twitch on the use of undocumented endpoints has always been that they are not intended for 3rd party use, and that they can and will change, break, or be removed, without any prior warning.
If you wish for Twitch to create endpoints that return the data you need that’s not currently available in the API designed for 3rd party developers, please suggest that idea so that Twitch can see what level of demand there is for such endpoints and if your use case for that data is legitimate https://twitch.uservoice.com/forums/310213-developers