That's a good rule of thumb for anyone (but if you have a quarter million in cash equivalents you're probably a business or super-wealthy).

I wonder if anyone has done a correlation study with bank failures vs CD/HYSA rates. The ones I know of that "everyone" flowed into have survived.

Kaupthing [1] was offering very attractive interest rates in 2007.

[1] https://en.wikipedia.org/wiki/Kaupthing_Bank

This seems like a fair assessment. Especially for all these tiny banks that are absolutely not too big to fail.