I can't remember the last time I thought about how "fast" a browser is except for edge cases like complex WebGL stuff.
I don't think focusing on speed will plug the gap of users leaving for other browsers except for the minority of us on HN. I can't remember the last time a non-technical person I know complained about browser speed beyond a website itself being slow.
Well, for me at least, I always recognize if a button click/UI interaction doesn't force a visible and immediate UI response. That's one of the main reasons why I switched a couple of years to Chromium and now back to Firefox. It really responds fast. I totally agree that there were _very_ few instances where I noticed a rendering time difference.
Are you using a vanilla browser or do you have a content blocker installed perhaps? There is a very noticeable difference in load times and I would definitely consider the former 'slow'.
I agree though, that rendering performance is not the bottleneck of the browsing experience.
I don't think focusing on speed will plug the gap of users leaving for other browsers except for the minority of us on HN. I can't remember the last time a non-technical person I know complained about browser speed beyond a website itself being slow.