bitcoin has many advantages
fiat has many advantages
That's why I don't see any reason to make comparisons.
for example:
fiat is recognized by governments which allows it to be used in countries, everything you buy uses fiat, people receive a salary using fiat, but there are maximum values for walking on the street with fiat, something that does not happen with bitcoin where the person can be their own bank
All these advantages will be happening to bitcoin soon if the massive adoption will continue. It may not replace fiat, but its a good alternative for fiat in the future. For now, the best advantage of bitcoin is to have it for financial freedom. And this is rare to happen in fiat, as inflation continue to depreciate the value of fiat. And while fiat is closely monitored by the government, with bitcoin you can have limitless opportunities without the authority monitoring it.
Not as soon as you think. Don't get me wrong I am all for Bitcoin as well, but fiat currency cannot be phased out. No matter how high the inflation rate are because there are still those who choose to use fiat currency as a means to access everything. Currently, we do not want to pay for a cup of coffee or a quick fastfood launch break using Bitcoin, because of the transaction fees and some people is too afraid that they might going to regret spending Btc at this current timeline.
I definitely would agree that Bitcoin and fiat currency could both co-exist for the longest period if time.
I think that's the final goal of bitcoin, to be accepted as a currency and to be a good alternative for fiat, knowing for sure that bitcoin won't replace fiat in the long run. Although there are a lot more advantage using bitcoin, but its undeniable that the majority are still trusting fiat because its the only legit currency approved by the government. And as long as the government continue to backed fiat, the use of bitcoin will never become mainstream.