Fiat uses plenty of power on it's own. All the ATM's and banks. Much of our money is actually just numbers in a bank and it's been that way for a while. Fiat needs banks and ATM's and card machines everywhere. What does crypto need? A wallet and some computers to verify the transactions. Those computers can be placed anywhere, including next to power plants and in ice caves.

As for the ponzi aspect...there are a lot of things that have similarity to ponzis, in that the new money pays the old. Affiliate programs sprang to mind. Of course, some are more ponzi than others. With affiliate programs, the older members invite newer members, giving a percentage of what they spend to those that invited them. Technically there are a limit to the number of members that you can invite. Eventually, you'll run out of people. Of course, that rarely happens. Nothing gets 100% adoption. In reality, you can invite people, some of which won't even try to bring in others, make plenty of money, and they'll use whatever the service is and likely be happy with it.

There are also stocks. The new money raises the price and eventually, the old money sells their stocks, earning a ton for being one of the first.

You seem insistent that the early adopters deserve this reward. In some cases they do. The early miners certainly deserved what they got, because they allowed Bitcoin to become what it is today. Of course, Steem proves that just because you were here early and have gotten a lot of SP doesn't necessarily mean that you deserve to be in a position of high SP. The reward for early adoption is often greater than it necessarily should be, but it rewards people for being there when others weren't.

Whatever the case, crypto does serve a purpose. You ever tried using Paypal? They charge you a substantial fee, don't care about your privacy, have shitty customer service, and occasionally seize people's money with little or no evidence.