Web slowness has much more to do with sites than with browsers. Where sites have accumulated Everest-sized balls of JavaScript mud, web engines have only become more optimized. If you visit “old web” style pages (Macintosh Garden for example) on old machines with modern browsers there’s no speed problem at all.
In the face of all that JS, there’s only so far a spiffy new browser can improve the situation, aside from maybe drop large chunks of legacy web standards but then you’re breaking large chunks of the web.
