Compare Reservoir vs. WordPress
Reservoir is a Drupal 8 distribution focused on decoupled content management. It is developed by Acquia, the company providing enterprise grade Drupal hosting and solutions.
WordPress is not a very modern PHP CMS and does not use Symfony or other components. It is very popular and earns it's position in the listing of Symfony CMSes.
CMSes vailable for comparison: BackBee, Bolt CMS, Concrete5, Contenta, Contentful, Cosmic.js, Craft CMS, Drupal 8, eZ Platform, Fork CMS, GraphCMS, Grav, Jarves, Joomla!, Kunstmaan, October CMS, Open Orchestra, Pagekit, Pimcore, PyroCMS 3, Reservoir, Spress, Sulu CMS, Symfony CMF, Symphony CMS