> I believe that the WebExtensions API is more powerful in the sense that it allows more complex blocking rules.
This is not really accurate.
The Safari content blocking API and the WebExtensions DeclarativeNetRequest API are comparable. The difference is that WebExtensions are JavaScript and can run in the context of the web page. With WebExtensions, you get DNR plus arbitrary JS, whereas the Safari content blocker API is native code and doesn't run in the context of the web page. The arbitrary runtime JS is what allows you to do things that you can't do with declarative content blocking rules.
You could also have a Safari content blocker with an optional WebExtension for additional functionality with no usage of DeclarativeNetRequest.
> You could also have a Safari content blocker with an optional WebExtension for additional functionality with no usage of DeclarativeNetRequest.
That’s exactly what AdGuard and some other content blockers do. The result is that content blocking works everywhere, but it’s most effective in Safari. As a user, I prefer that over the approach of uBlock Origin Lite, which is a pure WebExtension and doesn’t do anything outside of Safari. Too bad, because I prefer using uBlock Origin on other platforms.