The thing that is changing here is that the images are scanned on the device before being uploaded to the cloud, instead of being scanned on the server after they are uploaded to the cloud.
If it hasn't been a problem that Google has been scanning your cloud data for the last decade, it didn't suddenly become a problem now.
The scanning was already a problem. A lesser one, as not using Google or iCloud avoided it. Now I can't, because technically Apple can now look directly at the phone. No idea hey it is so hard to get that difference.
You should note the fact that everything on closed systems is based on trust. Apple has had always the opportunity to look directly on your phone. That does not simply change overnight when they add some feature. And currently they scan only those images on-device, which would end up into the cloud. You can avoid this scanning by not using iCloud.
The feature what everyone is afraid of (scan all in my device), is super trivial to add generally. Company like Apple can push it to public in less like week regardless if this Child Safety came first.
This new feature is actually really hard to develop, because they try to create E2EE system with backdoor. And they want to lock themselves out of this backdoor to prevent misuse.
If it hasn't been a problem that Google has been scanning your cloud data for the last decade, it didn't suddenly become a problem now.