Where did I say that?
You asked for an example and I gave you one. Go to Cuba, exchange your dollars for pesos, and you will get to see a currently defined exchange rate. The definition of "defined exchange rate" doesn't change over time.
But for some reason I am supposed to provide one to you for a virtual currency. Do you see the double standard?
Who is being intentionally obtuse now? Provide an old example of a define exchange rate for Bitcoin if you have one.
Since you seem to need everything spelled out: gold is denominated in bitcoin (contrary to your assertion) just as gold is denominated in dollars. The price is set by the market and fluctuates. There were times before 1933 when there was a de facto defined (your definition) rate for gold and 1968 for silver, but there has not been any since.
Since that is how all currencies currently work, except for a few thug currencies, then that makes bitcoin equal to gold or any other store of value since the value is defined in the same way as gold.