That's not totally true. Orion supports Chrome/FF WebExtensions, for example. The engine does (practically, even in the EU) have to be WebKit, but that's not the same thing as a "Safari skin."

There is Reynard if you're motivated too (Gecko-based, but it's not ready for prime time yet, and to get good performance you'll have to resort to some workaround to get JIT enabled, as it does not rely on Apple's BrowserEngineKit; one of the goals of the project is giving to not up-to-date iOS devices access to a modern browser).