And then we can move the goalposts to "more secure distro with GrapheneOS" which isn't part of the conversation until you dragged it out.
GrapheneOS typically ships security updates within a day. But most of Samsung's phones get quarterly security updates[1]. There will never be a primary source with a Samsung insider saying "we're fine with our customers being vulnerable to widely exploited security bugs for the next 89 days, in order to save our massive corporation a few thousand dollars a month." But their priorities are revealed by their actions.
If the statement "OEMs don't care about security" is trivially proven false, as you said, then you should be able to prove it trivially by naming even just a single OEM whose update cadence matches GrapheneOS's.
The numbers aren't zero, certainly. Nor does it imply directly proportional levels of effort. But they are incredibly obviously given wholly different levels of attention on nearly all phones, by nearly all phone manufacturers.
Your trivially proving things can't involve asking other people to prove the opposite of things. You've instantly backed down.
> And then we can move the goalposts
Why? You haven't done anything except ask others to do things. You've moved the goalposts from trivially falsifiable, and started begging.