I’m pretty sure this rule is only there to stop the hundreds of “flashlight” apps that used to exist. (Although, they appear to still exist) There isn’t tons of innovation or competition in “flashlight app” other than adding advertisements. There used to be a bunch of them that would only get popular out of necessity. The ones I’m seeing now in the App Store do seem to have non-default behaviors like “strobe light” at least, so they aren’t true clones of native functionality.

Apple isn’t using that rule to take down alternate weather apps, despite them having their own native weather app. There’s still plenty of QR code scanning apps, despite that being built into default camera app.