But if your proxy takes at least $10 of your currency every time you use it, you would expect people to look for a different proxy.

In your example, Bitcoin would obviously be the "old system" if everyone wanted to use it for moving money around, because there are plenty of more advanced alternatives that work far better.

So why is Bitcoin so popular? Because it's a speculative investment. A new asset class divorced from fundamentals, making it impossible to say when the value is too high. That's why people like it.