Maybe. Smart people assumed Lehman wouldn't be left to sink. It was. And it caused a lot of problems. And the people who realized afterward that it was a mistake are retiring right about now.

Lehman had assets of ~4% of GDP and was a pure investment bank.

JPM has assets of ~15% of GDP and has 66 million household clients.

I'll take the odds that it's too big to fail.

These are logical sounding arguments, and you are going to be right more often than not. But humans make these decisions, they made the decision to let Lehman sink and it was obviously bad in retrospect, and there were many folks who were opposed to the bailouts in 08.

There are better options than playing these odds. Spread across banks, hold short term treasuries etc. Treasury functions at a company exist for a reason.

True, true, but I don't want to take zero risk. I want to take some risk. For example, I do own short term Treasuries, but I want to borrow against them to short some stocks I don't like. And as soon as I have a margin account, my counterparty risk changes drastically due to how brokers work.