The "killer" feature is actually that it was rendering traditional websites NOT fine, but in a bunch of hacks that would force a specific viewport width where most websites would render with reasonable font sizes and double tap to zoom to paragraph would fix the remainder.

Specifically this "killer" feature would already break traditional HTML pages with just text (that were 100% responsive even before "responsive" was a thing).

The entire mobile HTML stacks is hack on top of hacks. Like everything else in computing, TBH...