I don't think any of these are strictly limited to Safari. As far as I can tell, every feature you mention could be implemented by the third-party browsers.
> Only Safari can have extensions
The Orion browser [1] supports extensions, although I suppose the App Store rules could prove to be a problem with executing arbitrary code as it hasn't run through the full review process yet.
> only Safari can have iOS Content Blockers
Brave blocks content and ads.
> only Safari supports Screen Time
There is new API [1] for this and I believe everything you mentioned is available to developers, although I haven't used it myself.
> only Safari is allowed to launch apps
This should be possible to implement by checking the `.well-known/apple-app-site-association/` and calling `openURL:` on matches. It might be difficult to know for sure if some apps were installed or not, but that doesn't seem to be the key issue here.
[2]: https://developer.apple.com/documentation/deviceactivity/dev...