Chrome may or may not be the best browser. But Google properties tying into Chrome as a platform (think sync, extensions, auth, captchas) and making it really difficult to switch away creates a situation where it's not all about choosing the best browser any more. This harkens back to the same anti-competitive monopolistic behavior that Microsoft got sued for in the late 90's.
The best browser isn't the fastest. It's the one you can trust to serve you and not some corporation or government that wants to control what you see and where you go.
The problem with forks is having to chase upstream. The dominant browser can keep making changes with reckless abandon. And the fork has to keep up with those, even if it breaks their own features, lest they become incompatible with the "standard" version.
chasing upstream is a lot easier than chasing web standards and chromes performance, especially if you are only interested in providing more powerful extension api and better ui
Saying we need multiple browsers, then using chrome or its clone actually makes the situation worse.
Also chrome is no longer snappy as it was initially.