There’s no way this can be true.
Apple owns various platforms that ship Safari/WebKit and it’s the only option on iOS and watchOS. They’ve shipped more than 2 billion (and growing) iOS devices.
And hundreds of thousands native iOS apps use WebKit views.
So there’s no way Safari is a fringe 3rd party browser and has a better privacy story regarding fingerprinting and tracking than any of the other major browsers, including Firefox.
Unless you’re on the W3C mailing lists and GitHub repos, you wouldn’t know how active the WebKit team is on the development and implementation of web standards.
The market of web browsers has become "who gets to set the default search engine makes the moolah". Bing marketshare and revenue is driven by how well Edge works and how it can stop the bleeding to Chrome. Changing the engine to Quantum does not solve the problem they were having in the first place very well.
Web browsing dominance is a single member district. Firefox and Chrome are the two major parties, and IE/Opera/Safari are third parties.
IE could have gone to Firefox to promote open standards and "back the opposition" so to speak. They chose, instead, the corporate behemoth behind the mobile OS they want a foothold on (presumably).