No it isn't, given the extent UWP is still used on Windows given the failure of WinUI 3.0/WinAppSDK to deliver something that has feature parity with it.
Windows widgets and the new badly implemented File Explorer are probably the only WinUI 3.0 applications, the remaining stuff is still pretty much UWP, while many third parties that still care about WinRT at all, are stuck in UWP due to missing features and tooling in WinUI 3.0/WinAppSDK.
As for the rest of your remark, it doesn't change the fact that those runtimes exist and have relevant differences.
Windows widgets and the new badly implemented File Explorer are probably the only WinUI 3.0 applications, the remaining stuff is still pretty much UWP, while many third parties that still care about WinRT at all, are stuck in UWP due to missing features and tooling in WinUI 3.0/WinAppSDK.
As for the rest of your remark, it doesn't change the fact that those runtimes exist and have relevant differences.