> 3. In lots of platforms, including MacOS (I didn't test newest version yet), Android, iOS, using "system-ui" will end up using exactly the same font as just use "sans serif" anyway. So it really has little benefit.
Certainly on my Mac, which has been the case for quite some time, sans-serif defaults to Helvetica.
Since Apple was the organization that proposed "system-ui", it doesn't make sense that it would default to a font that already existed.
Apple created San Francisco as a family of fonts for macOS, iOS, iPadOS, etc., which is why Apple proposed to the W3C the concept of a system-ui font that differs from sans-serif.
Android, newer Windows and macOS has specific fonts for system-ui.
Certainly on my Mac, which has been the case for quite some time, sans-serif defaults to Helvetica.
Since Apple was the organization that proposed "system-ui", it doesn't make sense that it would default to a font that already existed.
Apple created San Francisco as a family of fonts for macOS, iOS, iPadOS, etc., which is why Apple proposed to the W3C the concept of a system-ui font that differs from sans-serif.
Android, newer Windows and macOS has specific fonts for system-ui.