I agree it would be crazy to spend $5 billion / year to run a payment network used by 5 million users (that number is pretty low IMO). That's just wasteful. And if you think Bitcoin is just that, you've been reading some funny pamphlets.
It is in fact a decentralized peer 2 peer network that enables any 2 parties in the world to exchange value over the internet without the need for trust and a central authority.
Was email better than regular mail back in 1990? You needed a $5000 computer and it still took a long time, while a stamp only cost a few cents. What a waste of money, right?
In my eyes, the problem is exactly that bitcoin isn't nothing but an expensive payment network. It is often called a "cryptocurrency", but in my eyes it is a gimmick of an currency, when it doesn't have an independent mechanism for value stabilization. As long as it has to use fiat to give it value, then fiat will still be the only currency in the pair and bitcoin is just the temporal solution to transfer fiat. That is why, in my technical point of view, it is the same to hope for bitcoin to replace fiat then to hope for your car to fly to the moon. In this reality these things just don't have the needed mechanics for the job..
Don't take me as a pessimist by this. I think that in the future we will have an cryptoasset that is able to break this currency boundary and will be able to actually offer an predictable value without the need for the support of fiat value. Trying to wish bitcoin to do this isn't just constructive use of energy. All these false hopes and illusions will only make a big mess and the people who profit for it aren't exactly the good kind.
I also think that you can't compare the e-mail protocol to bitcoin protocol. One is a communication protocol, you can compare it to IRC if you like. Bitcoin is an financial protocol with a lot more complexities and different rule-sets.