Google forked from WebKit in 2013, at this point there might be huge differences between WebKit and blink. Someone more knowledgeable might add something to this.

Chrome (Blink) and WebKit are two different engines.

It's Chrome dominating, Webkit a somewhat distant second [1], and Firefox a third, quickly disappearing into oblivion [2].

[1] There's a huge number of weird versions of WebKit running on TVs and such.

[2] It's barely around 200M users, but it's bleeding users slowly and surely https://data.firefox.com/dashboard/user-activity and https://news.itsfoss.com/firefox-decline/

    * Blink (Google)
    * WebKit2 (Apple and some folks, mainly WebKit2Gtk)
    * Gecko (Mozilla)

    Microsofts Trident is dead, they now use Blink.  
    Operas Presto is dead, they now use Blink.
    KDEs KHTML (the predecessor of WebKit1) is dead.  

Google is dominating, pushing through Android, all Googles-Services and Microsoft Edge. A reason to worry because Google controls the Web and the Engine. Furthermore implementing an entire new engine seems an enormous effort. For instance Microsoft only allows usage of Microsoft Teams Web with a webbrowser based upon Blink. So were back in 2002?

WebKit features also WebKit2Gtk (Epiphany) and Qt5-webkit (Otter) with native integration. Both use the native toolkits, which is an advantage! Interaction with the open-source community around WebKit seems rather good and the engine is integrated by others. Gecko seems not to be integrated by others but by forks only? You remember when Chrome was considered slick and fast? Originally Chrome used the native toolkit on every platform. Now Chrome ships an own toolkit, similar to Firefox.

And? Maybe there is a new engine on the block:

https://github.com/SerenityOS/ladybird

PS: I think the Epiphany guys doing a nice job but need more developers. The upcoming release will support Web-Extensions.