To be fair, if you are 1to1 backed in USDT or anything else like a stablecoin, then you have to worry about nothing. Even if it's de-pegged for a moment, you would have 1to1 backing in the banks and you could just pay a dollar for it and make it go back up.
What Luna had was a situation where it wasn't backed like that, so when it dropped under 1 dollar, there was no dollar to pay for it to get it back up to a dollar, and that is why it failed. I always warn people though, USDT could crash too, the moment governments seize their money, this isn't impossible and in theory a possibility and a huge vast risk in the market.
It was algorithmic and doesn't have backing of real money. I agree with you, the peg is illusion and if it can be redeemed in the first place because backed by real money, everyone wouldn't become worried and sell whatever is left to recoup themselves from disaster hence the hyperinflation of $luna in attempt to back the UST. It is a fake stablecoin and everybody seems to have learned to not recreate the same thing, at least the founder do kwon is punished.