Chromium dominance is effectively Google dominance when it comes to the open web. That is a world where Google no longer has to follow any sort of standards body because it is the standard. Another commenter, snowwrestler[1], put it best:
>With full control of the rendering engine on all platforms, Google can stop engaging with standards bodies. Web rendering standards will become simply what Google says they are, even if it is to their benefit. Imagine AMP but on steroids. When Safari stops rendering mobile sites correctly, there will be lots of helpful friends and family (and ads) telling folks to "just switch to Chrome, it's a better browser anyway."
>Google could also ship their own root certificate list and take control of Web PKI. Imagine Symantec but entirely at Google's option. Play ball or get security warnings. This would allow an end run around the democratization afforded by Let's Encrypt, for example. Controlling 99% of the client end of TLS confers just as much power as controlling the CA end.
All of these items are built into how Chromium renders the web. The other Chromium derivatives will be forced to swallow these changes because what are they going to do? Fork and maintain their own browser engine? Bisect patches from upstream forever? How many of these Chromium forks will have the resources to maintain their own fork of something as complex as Chromium?