The first web versions of Outlook were plenty fast and usable on my then workstation (PIII 667 MHz w/ 256 meg). In fact, a lot of the web applications made 15 years ago were fast enough for comfortable use on Pentium 4 and G4 CPUs, because most used combinations of server-side rendering and vanilla JS. It was painful to develop, sure, but the tradeoff in place now is severely detrimental to end users.