As I already stated in this comment, I have developed websites on Jekyll, Middleman, Hugo, and Hexo so far.
The most complicated website that is built on JAMstack that I know of is Smashing Magazine.
In my opinion, Wordpress and SPG are two different worlds. The first one is a global solution with an enormous amount of themes, plugins, and solutions. In the last couple of years, the platform moved forward, and it has many great features, but there are still too many options, settings, and cluttering. SPGs are unique, they could be developed specific to users needs, they could be extended by some customizations, plugins, shortcode, etc. But delivering content over CDNs as static files, that is powerful. And it could be free if you are using Netlify free plan.
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