How to get username, total viewers, stream title etc WITHOUT getting streamkey?

Just don’t request channel_read, stream key is just about the only use for that scope.

Total number of views, follows, stream title and game/category are public and do not require specific scopes. Editing title and game/category requires channel_editor. If you need to determine who an OAuth token belongs to then you can use https://id.twitch.tv/oauth2/validate endpoint.