Drupal IS slow, but many "modern" sites in JS or Wordpress are pretty heavily cached too. There's just no beating "static HTML file served over CDN, with portions rehydrated".
Whether you generate that HTML in Drupal, Wordpress, or some other system, having to run code to generate it is always going to be slower than caching. Drupal is plenty fast for internal previews (i.e. when the server is not overloaded), but at the end of the day it's still a PHP app, and LAMP/LEMP is generally harder to scale up and across vs plain files.
And for what it's worth, a Drupal site cached behind Acquia/Pantheon/etc and their CDN can -- usually will -- be faster than an uncached JS site served from any single data center.
Whether you generate that HTML in Drupal, Wordpress, or some other system, having to run code to generate it is always going to be slower than caching. Drupal is plenty fast for internal previews (i.e. when the server is not overloaded), but at the end of the day it's still a PHP app, and LAMP/LEMP is generally harder to scale up and across vs plain files.
And for what it's worth, a Drupal site cached behind Acquia/Pantheon/etc and their CDN can -- usually will -- be faster than an uncached JS site served from any single data center.