Using more power[1] to process vastly more transactions makes it more efficient. There are over a billion credit card transactions per day as it is, and that doesn't include debit cards, wire transfers, BACS, Swift, PayPal, WU, AliPay, WeChat and all the others. And cash while we're at it, that's part of the system too.
[1]: Lets say it does, though transaction processing is only a small part of the financial industries. I don't even know how much the whole industry uses, let alone what fraction is transaction handling.
The problem isn't that proof-of-work "uses a lot of [energy]"; the problem is that proof-of-work only exists to waste energy.
"Fix[ing] our methods of generating energy" is a red herring, since proof-of-work will automatically scale to consume any difference. It's a Red Queen's Race, which cannot be won.
Bitcoin is a distributed consensus algorithm, and the way it establishes consensus is simple: pick the longest chain. Spamming dummy blocks on to an old chain will cause that consensus to switch, allowing double-spends, so Bitcoin requires PoW as an anti-spam mechanism to slow everything down by wasting energy ( https://en.wikipedia.org/wiki/Hashcash ).
I wouldn't go so far as calling blockchains "trustless", since PoW has its own vulnerabilities, e.g.
- Lottery-like incentives for mining favours centralisation, to reduce volatility. That gives mining pools a lot of control, e.g. whether to back forks or not.
- Centralised mining is vulnerable to existing power structures, e.g. those with deep pockets can purchase warehouse-sized mining rigs, can launch legal or physical attacks on the rigs of others, etc.
PoW makes it expensive to attempt a double spend. You can't practically double spend because it is too expensive to do. The high cost of PoW is what gives the network security from double spend. Therefore it is not wasted energy. It is energy spent to secure against double spends.
You could use PoS but that is centralized and vulnerable to manipulation just like fiat.
Slow depends on what you are needing the system to do. If you need to pay for groceries, then Bitcoin is slow. If you need to do remittances or settlement then Bitcoin is extremely fast - much faster to reach finality than anything else. Therefore Bitcoin is only really useful as a base layer of the financial world. But that is also extremely useful. Faster layers like Lightning can be built on top.
The traditional finance system easily does tens of thousands of times more transactions than cryptocurrencies. Visa alone does a thousand times more transactions than Bitcoin.
Cryptocurrency uses over 0.5% of the world's electricity to do less than 0.01% of the world's transactions.
So, no, your statement is wildly wrong. I have zero problem calling it a lie, because you made it up out of your head and made no attempt to justify it with facts.
Also you can transfer any amount in a single transaction, so the transaction value throughput in Bitcoin is still infinite. This makes Bitcoin useful as a secure settlement layer for other systems.
Both need to talk to each other over the network, but in the second, it's thousands of systems needing to synchronize the information.
What a stupid lie you're telling yourself to justify that "this is fine!".