Has drupal abandoned drush?
You have installed the development master branch of Drush. To continue using commands such as drush dl, drush pm-update and so on, you should install the 8.x branch of Drush.

However, your basic supposition is correct. The Drupal community is moving towards Composer and away from drush make and the drush pm-* commands. The reason for this is that more and more Drupal modules are depending on code that is distributed via Composer libraries. When using modules with Composer dependencies, the most convenient way to manage your Drupal site is through Composer. See drupal-composer/drupal-project for an example of this.

All of the other Drush commands are still relevant and remain useful.