Why isn’t it a waste? You say it like it is a fact ... what’s the logic there?
I see no benefit in a decentralised currency: gold is one (anyone can mine it) and there’s a reason we moved away from it.
I don’t buy that bitcoin is either decentralised (they who control the algorithm steering committee control the currency); trustless (why should I trust irreversible transactions? Why should I trust those who wrote my wallet? Why should I trust those that wrote my mining app?); nor robust (the domain of money is law, not logic, so always subject to government interference; the price is currently highly volatile; and apps always have bugs yet to be discovered).
And I'm sorry, I won't address your other points.
Let’s say I buy a widget. How can I trust that the widget will arrive? That it will do what widgets do? That it will not break? None of these are payment issues, but they might call for a refund. How can I get a refund? How can the refund system be resistant to abuse?
The answers we currently have are “the law”. If the law functions, I don’t need a trustless currency.