Without fiat bitcoin is valueless, because the value of each Satoshi is calculated in terms of fiat. Upon the reality bitcoin won't get into removal of the fiat from usage. There will be integrated usage, and bitcoin will be more popular among people as an investment same as that people give importance to gold by this time. Importantly the generation will be completely dependent to technology and this makes the growth of bitcoin to be very high than other form of long-term investments.
The value of bitcoin is calculated in fiat because we are still the one calculating it in fiat, just like you have it here, you are tying it to invests, but bitcoin is actually supposed to be a currency on its own, when you spend bitcoin, it should be bitcoin, but the problem which people have just seen with bitcoin is because of its limited supply, and people wonder how such limit could really supply the billions of people we have in this world if bitcoin is to succeed as the global currency, I dont know how it will but till it becomes global currency before we would be able to figure that out, but as you said, we still tie the measure of bitcoin to its fiat equivalent because we have not fully accepted the use of cryptocurrency as means of payment whole heartedly.