For a less biased result, use Stable: https://wpt.fyi/results/?label=master&label=stable&aligned
> If you look at the full WPT test suite [1], you'll see that Safari is by far the one failing the biggest number of tests, i.e. the most buggy browser.
In Safari's case, most WPT test fails mean "hasn't been implemented yet".
> Interop is only a tiny subset of the entire suite of WPT tests, and it only contains tests that all vendors agreed upon…
Exactly. If you're happy building "Works with Chrome" web apps, Safari is not for you.