It doesn't need to be possible.
>change system configurations
You can have an settings app to configure the system.
>then you have Android
Which is much farther ahead than Ubuntu on security. Ubuntu needs to play catch up.
>but then you have certainly not enabled everything a user can do with sudo.
The goal is not to be able to do everything. The average user doesn't need to be able to do anything. Especially with their regular account.