What you seem to be completely overlooking is that, on any membership site, visitors don't just visit one page. The significance of that is, after the first page loads, jQuery is cached in the browser. That means, for all subsequent visits to any other page on the same site, jQuery doesn't re-load at all. Ever.
So what you think of as a clever trick for speeding up page loading does nothing at all after the first visit. Absolutely zero. (You can easily check this by looking at your browser tools when you visit a second page on your site.)
This is a great example of what happens if you treat speed testing websites as masters instead of tools. They only test a page as a one-off. That is fine for some sites, but useless as a measure of any membership site (especially if the content in the site is completely protected). If you want to speed up membership sites, you need solutions that are persistently helpful, and that means using OPcache, transients, and wp_cache.
Speed testing websites also typically give some terrible advice for modern websites. But, since that actually would be getting off topic here, I won't go into them.