The valid question here is – what are the project details and business requirements behind building a SPA (Single-page application) website?
In case you are building just a single static page with no interactions or editability whatsoever, you may very well proceed with plain HTML, CSS, and JavaScript.
Successful websites that I can think of usually require (and even plan for) regular editing and continuous updates. In that case you will need a persistent storage that would keep track of your changes and authorized users (as you will need credentials in order to update content). The website would also need an administrative panel of sort, and management of all moving wheels.
Furthermore, the site may require certain integrations – be it a social login feature, a booking form, or anything else. Some of those could be integrated directly with embeddable scripts or simple libraries, but sometimes it simply takes a bit longer.
The more you need to build from scratch (which is provided in WordPress by default), the longer and more expensive the build would be, and requiring more time for Q&A and revisions.
You may utilize WordPress in terms of efficiency of implementation and control/flexibility. It will likely be heavier than a custom build, but depending on your setup and monthly traffic, the difference may be 200–300 milliseconds at worst which can easily be cached so that recurring visitors won’t see difference after their initial load.
