We can pick and chose whatever area we decide to view identical or diverging. The fact of the matter is this: https://web-confluence.appspot.com/#!/confluence

- Chrome: 7602 web APIs

- Firefox: 6572 web APIs

- Safari: 6335 web APIs

(Web APIs include everything, including CSS, see API catalog at the top right of the page).

If anything, Firefox is identical to Safari. This is especially evident if you look at the "browser-specific" tag

Safari is adding 150 to 400 new APIs with each release. It's harder to see this because their cadence has historically been tied to new OS releases (so, yearly, and really wish they'd increase the cadence). Meanwhile, in the latest version alone Chrome released 75 new APIs. And they release 20 to 70 new APIs in every version which they release monthly [1].

Yes, Safari may be less prioritized than other teams at Apple, but in no conceivable way, shape, or form are they "the new IE6".

[1] https://www.chromestatus.com/features/schedule