I dont think websites is a good example, Javascript barely existed back in the day, now you've pages that look like animated books as you scroll. Videos also used to be 120p, now they are 4k.
But I'm at like 2-5% cpu usage with firefox and many tabs open, KDE, a file manager, and software center; most of the usage seems to be from the task manager itself. I think its likely some high level language like Javascript slowing things down, which is done to sandbox things and sterilize third party code thats run without vetting.
I remember an ad Intel made about how AMD was "gluing their chips together", being the chiplet design. In the end ram speeds continued to improve and thus the bottlenecks were alleviated, and now every design is the same.
I switched my company over to Bitwarden because it was open source, any the code could be vetted. I'd definitely be dropping it if they ever started making things proprietary.
We got burned by Lastpass and it was an easy sell.
I kind of think Ubuntu or Fedora with Gnome or KDE will be the best, given the support and development.