Web performance doesn't need any of that. Browsers are very good at parsing HTML and CDNs are a commodity now. A directory of HTML files is about as fast as it gets, no preloading necessary (and you avoid all that JS payload too).
It really depends on your network connection. If it is fast fetching a small HTML page is nearly instant, if it
s not then it will be noticeable compared to locally cached data.
Now you don't need to do it as complex as Gatsby does, you could literally just GET the HTML file and throw away the result so that it is in the cache.
What if you want to make a site-wide change (e.g. GDPR mandates a cookie banner)?
With Gatsby's approach, you only modify the js that renders the template. Then, if a site-wide change needs to be made, you make a single change in the js template.
With the static-HTML-served-from-directories approach, you would have to rebuild all the HTML for your entire site if you wanted a template change and a database to store all the articles/posts for you to rebuild the HTML.
