Short answer: hell no. What gives currency value is how often people use said currency to purchase goods, nobody uses Bitcoin, not to the extent of any real currencies anyways.
Bitcoin will probably never be a currency equivalent to fiat, but it surely is a store of value in the long term.
Yes. But they don't remotely justify its value, which has been established long before its technological applications.
No, gold is not a currency (anymore). Gold is an asset. Gold is rare. Gold has real world use. Gold can be used for many things. Gold can be purchased with money to be worn or used.
So no, by that logic, gold shouldn't be worthless at all. You're comparing two different things.
Most people would probably disagree on that. Gold even has an ISO-4217 currency designaton, XAU.
Credit rating agencies are using gold reserves(among other things) so this could be a reason
As far as I know, none of those countries promises to redeem bearers of banknotes with an equivalent value in gold, which is what being on a gold standard means[1].
Plenty of central banks have gold reserves, that's basically a vestige from the past, but that's not the same as saying the currency is backed by gold.