When I was at university I tinkered with writing a MUD app that ran on telnet over a modem that would echo back inputs. It was incredibly slow once there were more than 4 or 5 users because my code sucked. I can't use that as evidence that modems weren't fast enough.

It seems obvious that how quickly a web page can refresh is entirely down to the skill of the developers who created it. There's nothing inherently slow about a web page - plenty of pages update quickly enough. Browsers are fast. Some userspace code is not. If you're using a page that doesn't work fast enough that's down to the developer, not the web itself.