How to customize the homepage title without creating new pages?
By default the homepage for D8 is set to /node (similar to D7).
And unlike Drupal 7, this is a view. So, adding a title is as simple as adding the title to the view. (Views in core, yay!)


Go to /admin/structure/views/view/frontpage.
Add title to the view
Save


It is as simple as that!
If you save any other page as your homepage, then you could set the title to the route as you have already specified in the question.