Both things can be true - a person can prefer a more complicated and feature rich UX, while most people prefer a simpler UX that doesn't provide as much control.
You can definitely have a simple to use UI that still has all the same complex functionalities of an esoteric one. The more advanced features will just be more hidden away. To me, the only real advantage to an esoteric UI like calibre is the ability to do things faster and easier once you have learned it.
But honestly, for that i prefer a CLI.