Bitcoin is not an IOU. No one owes you anything.
Of course it's an IOU. It's a valueless token that you pray someone else honors the value for. That's the very definition of an IOU. An IOU doesn't require a contract solely with one other party. You have entered into a far worse contract, a contract with no discernable party at all.
The only type of money that isn't an IOU are physical commodity currencies whether it's silver, gold, oil, wheat, or what have you, because even if every single other person on the planet dies, you do not require any external actors to make good on your claim and are already holding it in your hand. It is not possible to be left "holding the bag" with a real commodity currency. Since bitcoin is not a real commodity, not tangible, and is essentially an imaginary object, it is very much an IOU as far as the human plane of existence is concerned.
