1. There are penalties for underpayment of estimated taxes. And there are even interest charges on penalties. https://www.irs.gov/payments/underpayment-of-estimated-tax-b...

2. The triple tax advantage is not ridiculous. (1) and (3) are not the same thing. 401k for example is not taxed going in (you fund it with pre-tax dollars) but is taxed when taken out. When you withdraw money from your 401k in retirement, you owe taxes on the capital gains that have accrued in the account since you first put the money in. But if you take money out of HSAs for paying medical bills, there is no tax on the capital appreciation you have enjoyed in your HSA account.