The difference is that the extension platform itself is open. I can compile Chromium and create/install/redistribute extensions all without ever asking for Google's permission, and still have an acceptable user experience on non-Windows platforms. Afaik, Edge doesn't allow easy extension installation prompts from third party websites.

Yes, redistributing extensions for Windows Chrome users (not Windows Chromium) does require the Chrome Web Store. This is unfortunate, but at least Google has a better track record when it comes to banning extensions that modify their things on their own web properties.