There's a lot in the news about the energy cost of Bitcoin recently. Recently Elon Musk talked about "currencies using <1% the energy per transaction of BTC".
This page provides some values for comparison:
Kilowatt hour (KWh) consumed per transaction
XRP
0.0079
Dogecoin
0.12
Cardano
0.5479
Litecoin
18.522
Bitcoin Cash
18.957
Ethereum
62.56
Bitcoin
707
My understanding is that coin generation gets more difficult the more coins are mined, so I'm wondering is Ethereum for example actually 10X more efficient, or has it simply not been around as long so the calculations haven't grown in complexity?
Are energy costs per transaction for all these currencies going to scale with number of transactions in some well-defined way, or have I misunderstood?