For a larger websites a good CMS can make things easier. But it will be slower. I made benchmarks. I have created a website with typo3 (php) and my PC could serve 30pages per second (without images etc.). The same website in a static HTML version (the user does not see a difference) could be served by the same PC around 3000times per second which is an increase of 100x!
Drupal is much faster than typo3, but a static HTML will be always faster.
I programmed a simple CMS myself that creates static pages if possible which are then stored on the server. With this approach it is very fast, but also not as flexible as a normal CMS.