In 1999 I had a cable modem connection that could pull down 2 megabytes per second and ping up and down the west cost well under 50ms.
But forum servers were slow. Like, really really slow. When Sites like Reddit finally came to, 15 or so years later, with inline replies, they were a breath of fresh air.
Back in 99 Slashdot had massive resources put into making it responsive, lots of servers thrown at it, and it was still laggy and slow compared to Reddit now days.
Everyone arguing about "time to first draw being under 100ms" forgets that just a short time ago, web servers took more than 100ms to respond to a connection.
In 1999 I would have been jealous of your internet connection — I still had a 256kbps ISDN line, and there were fast forums even then (but mostly not). I think it mainly depended on whether the sites rendered HTML on the fly (with like maybe Perl? to render database content) or... just served static HTML.
Page reloads only got expensive when we decided that they would do a bunch of other shit besides that.
And yet, once you wait that 100ms or however long it takes for the server to respond, your page is fully loaded and interactive. During the loading process, your browser remains responsive and your CPU is not loaded.
Nowadays, we still wait the same amount of time for the initial load, but now your CPU is at 100% parsing megabytes of shitty Javascript, and once the initial load completes, you're still not guaranteed the page won't slow down/overload your CPU again because some stuff can be asynchronously loaded (supposedly for performance reasons, even though doing it on the backend as part of the initial load would be faster in the vast majority of cases).
