Yeah but it gets a little bit out of hand as i think. Payment systems like Paypal that are indeed secure, don't need nearly as much power. And with every Bitcoin that is paid to the miners, mining gets less profitable unless the value of Bitcoin goes up. Until there are no new bitcoins and the miners are paid from the transaction fees.
I actually think Steem and Steem Dollar have a better chance of becoming a main currency, since their value come from the content creators and the stakeholders plus the proof of witness technology needs way less energy.
RE: Bitcoin use case in my view and why he will stay the KING