When Musk announced the release of the current NAV software, he claimed Tesla would be able to add more functionality to the navigation software - something that was difficult with the original software they licensed from Garmin/Navigon.
But it's been years - and we still don't have features present in other navigation packages - such as adding waypoints or route customization (selecting alternate routes).
It's likely Tesla is doing with NAV what they've done with their other software apps (with the exception of AP/FSD) - once the software is released, very few changes (if any) are made to the software - and when the changes are made, they're usually cosmetic (related to the user interface).
So, we haven't seen much improvement in the navigation app since NAV 2.0 was released, while other nav apps have continued to evolve, adding new features.
While adding screen mirroring (or Android Auto/Apple CarPlay) could provide more 3rd party apps - such as Audible and better media players, that isn't the solution for the navigation software. The nav app needs to map charging stops plus have integration with AP/FSD - something that would be difficult to get with 3rd party apps.
Since we're stuck with using Tesla's navigation app - we'll only see improvements if Tesla will assign developers to add the (long-promised) missing features and improve the routing functionality.