I am referring to the on device flavor - if it does not apply to macOS that is great.

The server-side version is strictly less private.

Only if the client-side scanning includes end-to-end encryption, which was never part of the deal. It was a possible future feature. Also, only if the-client side scanning only scans images being uploaded to iCloud and not literally everything.

Also any kind of content scanning is always strictly worse than no scanning at all.

The proposal was of course to check only images being uploaded to iCloud.