One thread for JS main loop, one for the DOM, others for network requests… Browsers on regular web pages are already quite multithreaded.
Modern Chromebooks do a lot more than just run a single website or a single web app - for example right now I am replying to you in Chrome browser but I also have a docker container running doing some dev work in the debian linux console on a separate workspace.
A use case that is meaningless for 90+% of chreombook users.
Interested to see your data - can you share a reference? Thanks!