I would be comfortable keeping hundreds of millions in a US bank.
FDIC insurance has pretty much never been pulled, the "failed bank" doesn't give you any insight into this, instead the FDIC uses the capitalization information of all the banks it has oversight over and uses that to act as a broker for sells before the insurance is needed.
They just get on the phone with a bigger bank and say "hey you wanna buy this massive pile of crap and mismanagement for pennies on the dollar with an assurance you'll avoid any antitrust issue or prosecution for fraud from this new subsidiary you'll have?"
And the bigger bank is like "woah all those customers and their info and people that think they have free checkings account? we can make all this money back in the first month!"
and all the balances are placed in the bigger more heavily capitalized bank.
In 2008 the big banks also had trouble, and it was pretty skillfully managed, note that FDIC insurance would not have been able to cover a big bank failing, it is a confidence scheme just like everything else. And the the consolidations occurred for the next 6 years. There is nothing proven to prevent losses during 2008's great financial crises, or a worse scenario, there are things that fortunately didn't happen.
All of this is before you have to worry about those insurance ownership categories. Because you're right, that is very nuanced!
It's either: FDIC insurance won't matter (small bank failing), or, FDIC insurance won't matter (big bank failing). And so given no proven alternatives, I don't worry about it.
You can min/max by having 100s of bank accounts with a max of $250k if you really want. I'll pass.