Is it though? Gold in vaults easily outstrips the value assigned to all bitcoins and I doubt these vaults use even 1 Twh/year. Vaults are only environmentally expensive in construction. And since we have a surplus of vaults and bunkers (from digitization of stock trading and the end of the cold war, respectively), the only cost is protection. A few guards and some cameras and high security doors can protect >$10mio worth of gold, probably not using more energy than a few households. Managing a farm of ASICs for Bitcoin generating that amount is probably more labor intensive.
That's only because Bitcoin is still relatively insignificant blip in the world of trade, mostly a pastime for gamblers and scammers. It's footprint is actually absurdly huge compared to value it provides.
The real problem is scaling. Vaults, guards, banks, lawyers scale somewhere around O(n) to O(n logn) with the size of the market. Bitcoin's proof of work - the means of securing it - scales, to the best of my understanding, as O(n!) with the number of miners. That's not something you can run a global economy on.
On the contrary: the purpose of private banks is almost exclusively for billionaires to move their wealth around, while externalising costs to all of us. Many financial market interventions in the past are the society bailing out billionaires who bet irresponsibly and cannot bear reducing themselves to millionaires.
Compared to a free domestic ACH or wire?
Internationally you have to pay exchanges on the receiving end >1% fees to convert it to something you can actually spend.
I'd guess you'll lose far more than doing the same with gold, because the market slippage due to lack of liquidity far exceeds the cost of those vaults, banks, and guards.
A trade of $10M, or 1250 bitcoins, would move the market by 6%
After all these years of growth, Bitcoin's market cap becomes its own unique edge. One simply cannot transfer significant amount, say tens of millions of dollars, easily in any other crypto currency.
The cost of energy is minuscule compared to alternative means of achieving the same: vaults, guards, banks, lawyers, etc.