I'm a long way from 12TB, but I was relieved to see the new plans since I know I will eventually pass 2TB. As you mentioned, I consider iCloud basically for syncing and short-term backup of convenience, but I wouldn't trust it as a single point of failure for anything.

Photos I take with my real camera are backed up separately on a computer, separate drive, and off-site (Arq Backup to Wasabi). Photos I take with my phone are synced through iCloud to a computer with "Download entire library" enabled, which then has the same local and offsite backup.

The iCloud syncing has gotten more reliable over the years though in my experience. So I'm increasingly comfortable with it, but I'd still never fully trust my priceless data with any of the easy-but-no-control mainstream services like Apple or Google Photos.