I think you're missing the point. We're not comparing Safari with IE6 -- that would be absurd, we're just saying Safari compares to it's peers (Chrome, Firefox, heck, even Edge) like IE6 used to compare to the other browsers back in the day: stuff would mostly work on everything else but always needed special attention/polyfills/workarounds for IE.

On the project I currently work on the codebase is _littered_ with workarounds and hacks to get stuff to work on Safari.