Well there's a bit of a problem there because it's not quite that simple. Photos.app is completely opaque which means it is very hard to validate the integrity of what is in there. As a point, it's not a backup until it is validated and the restore is tested. The originals are stored verbatim so that's less of a problem but the layers of edits and metadata changes over the top is what you risk losing and those are almost completely impossible to extract from it, even if you have the SQLite data file behind the scenes.
On your second point, I had exactly that as well and had to repair the library. Worrying.
I'm copying everything out into (don't laugh) OneDrive at the moment. It syncs immediately to my PC where I can do a hard backup to an external NTFS volume and can actually validate it against that. I don't need much other than gallery folder names which you can export the structure of with some futzing. I've dumped a hundred or so edits out flattened as well.
There are some photos that would destroy me if I lost them so I am ultra paranoid about this.
Sounds like you are ready to ditch the Mac altogether for your sanity.
I really don’t understand your level of worry.
To keep regular backups is the best thing you can do in any environment, and even then things will go wrong from time to time.
I still remember when I was still on Windows, 15 years ago, finding out that some of my photos original RAWs having become corrupted and all my backups having the corrupted version on them.
When you have thousands of files, this is always a possibility and that’s why these days, once a backup disk becomes full, I often just swap it with a new one and keep the old one as archive.
Opaque or not opaque, files get corrupted from time to time.
It happens on Macs, Windows PCs and Unix workstations, on iCloud, on OneDrive, Dropbox or whatever else.
If your data is important to you, you must have a solid backup strategy.
If you think avoiding Photos, iCloud, Reminders and Notes is going to save you from trouble, good luck to you.