Formally, proof-of-work crypto is proof-of-energy crypto, and energy is perfectly valuable thing. The problem is that you can't extract that energy back to utilize it for your needs.

Proof-of-stack crypto is obvious scam, so not need even to take it into account.

There could be another crypto with proof-of-networking, i.e. mining occur when node service network long enough, i.e. you getting new coins for supporting network activity and availability. It shoud be much less energy hungry, with much more sustainable network and nearly instant transactions. This will be "proof-of-time" kind of crypto.

In any case crypto, while backed with some real values like energy or time, which means every single coin was not made "from air" like fiat, still have a problem with extracting its value back. It's like making coins from gold without ability to make a raw gold from coins.

So, there is still long enough way for independent currencies to go. Wile it have limited, but decent use as an alternative payment system, crypto is in no way perfect. It's just a beta version of independent currency.

Precious metals are far from perfect too. Just a simple problem with precious metal verification, when you don't have a simple way to check if coin/bullion is really made from precious metal with necessary purity makes gold limited currency too.

Formally, proof-of-work crypto is proof-of-energy crypto, and energy is perfectly valuable thing. The problem is that you can't extract that energy back to utilize it for your needs.

Proof-of-stack crypto is obvious scam, so not need even to take it into account.

There could be another crypto with proof-of-networking, i.e. mining occur when node service network long enough, i.e. you getting new coins for supporting network activity and availability. It shoud be much less energy hungry, with much more sustainable network and nearly instant transactions. This will be "proof-of-time" kind of crypto.

In any case crypto, while backed with some real values like energy or time, which means every single coin was not made "from air" like fiat, still have a problem with extracting its value back. It's like making coins from gold without ability to make a raw gold from coins.

So, there is still long enough way for independent currencies to go. Wile it have limited, but decent use as an alternative payment system, crypto is in now way perfect. It's just a beta version of independent currency.

Precious metals are far from perfect too. Just a simple problem with precious metal verification, when you don't have a simple way to check if coin/bullion is really made from precious metal with necessary purity makes gold limited currency too.