How do I define a route and controller for the home page?
This is a classic case of trying to do something in the non-Drupal way -- conceptually, defining a custom route for your home page route makes sense, and it's possible in other frameworks, but Drupal has a different way of doing things that makes this approach completely unintuitive.

Here's how to do it:


Define your route as something other than '/' (i.e. '/students/overview')
In /admin/config/system/site-information, set your "Default Front Page" to whatever your route was:




Voila!