True. But for average people at popular banks, it's very sufficient.

It's fairly trivial to make sure everything's FDIC insured, and being wealthy enough to care about the per-account caps should mean you've got someone to advise you on doing so.

It doesn't even require a human advisor. Many banks participate in CDAR, which spreads large deposits across multiple accounts at other banks in the network. Fidelity isn't a bank, but their cash management feature includes checks, an ATM card, bill pay, and can send and receive ACH and wire transfers; they also implement this hack.

None of this applies to securities. Presumably you could insure them. It's not obvious to me from first principles that the cost of insurance would wipe out any incremental appreciation value, but I've never heard of anyone doing this so probably it does.

Securities held at a broker are usually backed by SPIC protection.