It's funny because different people would interpret this sentence differently.
If you have high level understanding of the tech behind it, this feels like a threat. But if you don't, this sounds like an honest message from someone who genuinely wants to protect you.
A regular user log into Google account and see their photos today. Tomorrow they log in and see the photos again. And they would assume this system will always work like this.
This actually happened to me - a decade ago or so, Google suddenly did not allow me to access my Google Mail unless I provided them with my phone number for "additional verification and security". I had got a job offer and was desperate to access my mail and so caved-in with a lot of resentment. (Ofcourse, now it is nearly impossible to create a Google account without a phone number, but in those days people considered phone numbers to be private and were leery at services that demanded it for sign-up). And then, later on they suddenly stopped allowing you to reset your passwords using email and security questions unless you provided them even more data for "verification" (which nearly often wasn't enough to allow you to recover the account).
Self-hosting will become the norm very soon.
I think the usual bottlenecks of "hard to manage, no backup" are no longer there. There are very good managed self-hosting solutions so you don't need to worry about anything.
You just run your immich instance and you're good
I’m not sure I understand why this particular line bothers you. They seem to just be emphasising that your Google account has a lot of information and therefore they are providing another way to secure it?
Whether this is a good method or not is a different discussion and I probably will not use this method
If you have high level understanding of the tech behind it, this feels like a threat. But if you don't, this sounds like an honest message from someone who genuinely wants to protect you.
A regular user log into Google account and see their photos today. Tomorrow they log in and see the photos again. And they would assume this system will always work like this.