This is in fact a major issue. In my IPhone 5SE I am on 2000 out 70 000 after one week. I decided one week ago to upgrade my Photos to iCloud, to optimize space and sharing, but this is crazy. I understand the option of making the recognition on the devices instead of doing it on the cloud (as does google) for privacy reasons. But some processing features should be shared between devices in the same iCloud account in order to avoid the recomputation on all devices,... this way it seems dumb. And something is in fact shared, since the persons are automatically created and shared between devices, but not fully updated. Or so it seems...