I wasn't just blindly assuming the alias worked the same. I actually read the Compare-Object documentation [1], which contains that exact command as an example of how to compare files. I just didn't understand the sort of comparison it did.

If you search "PowerShell compare two files", it becomes pretty clear this is a common confusion even among people using the name Compare-Object. For example, the top serverfault question has an incorrect top-voted, accepted answer [2].

[1]: https://docs.microsoft.com/en-us/powershell/module/microsoft...

[2]: https://serverfault.com/a/5604