It could be.
Honestly, it could go either way.
Whether it’s worthwhile to run Drupal or not depends less on the number of pages or size of the website, and has far more to do with other factors such as the complexity of the pages and site itself.
Whether Drupal is the optimal choice to power a website depends on what it needs to achieve, and whether Drupal as a CMS best meets this need or not.
In many ways, Drupal can be seen as a CMS heavyweight, carrying lots of functionality with it out of the box. This is especially evident when comparing the CMS to its popular open-source competitors.
For website pages that simply aren’t made of much — let’s take simply styled long walls of text, for example — Drupal could, potentially, pack in more punch than is needed by the website.
However, if there are elements to the site that, perhaps, demand frequent updates, or are tasked with a constant turnover or churning of content, you may find Drupal a better fit than, say, WordPress as a CMS.
Of course, this could be for many reasons, and multiple factors play in, both large and small. After all, managing a website and its content is just as much to do with minor details in functioning, as much as the overall display.
Drupal is in many ways superior to its popular open-source competitors, not least that its strengths lie in harmonizing content.
Arguably one of Drupal’s greatest strengths is its ability to break down content into various elements and fields, which allows content to be interchanged, linked and referenced all through the website (or application) with ease.
Drupal’s rich use of taxonomy terms and vocabularies, content types and respective nodes, and blocks which can take advantage of custom fields makes creating and displaying highly intricate content painless.
Views, which now ships with Drupal 8 (though previously a separate contributed module in Drupal 7) allows for even greater flexibility with regards to accessing elements and fields within nodes, taxonomies, and blocks.
There is an infinite number of field types available in both Drupal 7, and Drupal 8 in particular, and contributed modules and patches alike make this availability even broader.
This, coupled with other potential contributed modules such as Display Suite and Panels, make even more possibilities available with regards to the storage of information in fields and elements.
Content can be cross-linked into web forms, blocks, and Views, which combined can form an endless number of possible ways to display and organize content.
The Views module has grown from strength to strength since its release, and as of now allows a Drupal website’s content to be displayed, filtered, refined, or dynamically organized in a multitude of intuitive ways.
Views also opens the possibility to expose field grouping or categorization to the end user, making them capable to choose what kind of content and the order in which it's displayed.
These possibilities are all made available in Drupal 7 and 8 pretty much acceptably out-the-box, whereas competing content management systems will require time and much custom code to build this functionality in.
The more you rely on custom code, the greater the risk of vulnerability, generally, particularly if you are coding for additional functionality. It becomes a risk concern also with regards to the future compatibility of software versions to the CMS.
So, in essence, Drupal could very well prove to be the perfect choice of CMS to power a website consisting of a single page, or indeed a website with hundreds of pieces of unique content.
In the same light, an alternative CMS such as Joomla or WordPress could be a better fit for a website consisting of thousands of pages. It simply depends on the kind of website, the nature of the content it serves, and how the end user will be interacting with the site to access information.
In conclusion, the number of pages or the size of a website shouldn’t be the sole influence for which content management system is best suited. What makes Drupal desirable as a CMS is based on a variety of factors, including, but not limited to, the size of the website in question.