And please do feature detection

I'm not sure how you'd do that with safe area insets. You could check for zero but some modern devices megitimately have zero safe area insets. Capacitor itself has to check Blink version for the SystemBars plugin.

But the app works fine with a “too old” webview. Why warn about it?

If you go into dark mode the status bar will be white with white text, because safe area doesn't work properly.