I think you can only really fairly compare the energy use to the physical infrastructure of the $USD (and/or other currencies) because the defense of the Petrodollar also defends general energy usage which all industries and organizations benefit from. Oil is used for plastics in medicine, computers, cars, fuel, fertilizer, you name it. The defense of the Petrodollar would be a defense of all of those things. From an energy standpoint can you fairly proportion out what energy is used to defend the $USD by industry or in a more succinct way?
The fact that Nvidia can create chips for GPUs, and Amazon can package them up and deliver them and all your other computer parts to your front door is also subsidized by the Petrodollar. Everything is!
If the U.S. just stopped defending the Petrodollar, it's not like the $USD just goes away or ceases to be valuable. The fighter jets don't disappear or stop being made.
It's also slowly becoming outdated. The U.S. is a net exporter of energy and the shale revolution has made the Middle East just a bit less important.
Anyway - I don't think it's a great exercise to compare Bitcoin energy usage to the "energy usage" of the $USD exactly because it's so difficult to really measure. You also have to think forward a little bit - as cryptocurrencies proliferate more companies will arise around new technologies, custodianship, etc. so when we talk about some abstract number of people in an office now supporting the $USD, we have no idea what the future number of people supporting the cryptocurrency networks will be in the future - it might actually create more jobs and more energy usage.
I see one real advantage to Cryptocurrency: protection against government misuse of monetary policy.
But aside from that, it's still up in the air for me to see how things go. The $USD is a pretty good currency (mostly holds value in the short term, accepted everywhere, highly liquid), but it isn't a phenomenal store of value. All of these fiat currencies and cryptocurrencies are going to be competing in an arena and it's going to be interesting to watch.