Maybe I'm wrong, but I have never seen Apple or Google suggest that someone use the parental control tools on a vulnerable adult person's phone to prevent them from hurting themselves. They have never run such a campaign for awareness or changed those tools to make them more palatable to controlling adult's phones (these tools are always sold as things to enable on a child's device). So no, I don't think we've started with that. We've started by adding some toggles and scary warning, and I agree that hasn't worked. I never suggested we stop trying, I suggested we allow the trusted owner/admin of the device to be more easily assigned to someone that person trusts, not just forcing Google into that role without consent.
You do not want to live in a world where that's normalized. There are legal processes for determining when somebody's "vulnerable" enough to need a guardian. Those process are heavy and strict for a damned good reason. And sometimes still not strict enough.
If I'm drunk and give my friend my car keys and ask them to not let me do anything stupid, I'm not giving up my legal rights to autonomy. I don't think this is any different. Legal guardianship is entirely unrelated, unless we're having some slippery slope fun.
So you expect aging parents to actively ask their children to put controls on their devices, and not to reverse that decision when it matters most?
Many, probably most, of the people most at risk aren't going to do that.
When you're (somewhat) drunk, you know that you're drunk, and you're still able to comprehend how that will slow down your reactions while driving. When you're being scammed, you think you're right... and if you begin to doubt that, you may tend to push the thought out of your mind rather than follow it through, and to evade things that might bring it back. And it's very hard to admit to yourself that you're permanently impaired in that sort of way... especially when you're impaired in that sort of way.
I'm expecting us that come up with something better than "give all computing control to two US companies" Yes this idea has flaws that you're an expert at picking at, but there's gotta be some middle ground that doesn't treat all of us as the most tech illiterate or scammable people.