> Then they moved to iCloud or manual sync and your forced to manage individual files again. Delete in iCloud, it’s gone everywhere. Want to keep your bad shots, but not have them on every device? Figure out how to move photos between multiple libraries while only being allowed to have one open at a time.

I don’t understand that. If you use iCloud, the cloud is primary storage, and your disk caches recently accessed cloud data.

So, just keep everything in a single library, and if your disk fills up iCloud will remove pictures you haven’t accessed recently from your disk.