Why not fix this at the browser level? E.g. long or double click on back button = go to previous non-javascript-affected page (I mean by that: last page navigated to in the classical sense, ignoring dynamic histories altered by js and dynamic content)

Double clicking is not a fix because it doubles latency, and more than doubles latency if you don't want to issue page loads that are immediately aborted. Long clicking is such a bizarre anti-feature that I never considered it might exist until I read about it in this HN discussion. Putting touchscreen-specific workarounds for lack of mouse buttons and modifier keys in a traditional GUI app is insanity.

That wouldn't work because this technique messes with your history. Long press on the button will just show you a list of the previous pages you visited, and all of them will have the same link to the one you're in, with just one at the bottom of the actual URL you came from. But that's so much friction UX-wise.