Browsers aren't single threaded, so the ST performance isn't the end-all-be-all metric to use. JavaScript is single threaded, but the browser itself uses multiple threads. E.g. there is the main thread, which handles the user input. There is the rendering thread, which actually takes up a majority of the CPU time on a lot of websites. And then there is stuff like GPU acceleration, which makes a lot of the web performant when it wouldn't be otherwise. Of course, a server does all of these things worse than a decent laptop.