Sure, and I was also around when XMLHttpRequest was new and innovative. And development then was awful compared to where webdev is today - I've been in the industry that entire time.
And it's not quite the same thing - we're not talking about injecting server-side HTML snippets into other HTML pages (which never actually went away). This is more like optional, self-contained but fully-featured web applications that load after the full HTML renders. You could use that to fetch static HTML, or you could use it to provide an interactive client-side experience that only operates on a portion of the page, up to whatever complexity you like. And if the user has JS disabled the rest of the site still renders correctly.
> it's literally what we used to do with XMLHttpRequest in IE 5/6 20+ years ago.
We generated page partials (or used static ones) and pulled them in with "Ajax" (for the oldies out there) and then inserted them in the right place on the page using innerHTML.
That’s not what Astro is doing, or how it’ll mostly be used (though you could do that)
And it's not quite the same thing - we're not talking about injecting server-side HTML snippets into other HTML pages (which never actually went away). This is more like optional, self-contained but fully-featured web applications that load after the full HTML renders. You could use that to fetch static HTML, or you could use it to provide an interactive client-side experience that only operates on a portion of the page, up to whatever complexity you like. And if the user has JS disabled the rest of the site still renders correctly.