Having both cryptocurrency and fiat are better that only choosing one. You still didnt notice but we are now living in a world like that. It also give us more option foe the different wants and needs of people. Some people doesnt want to have change thats why they want to stick with fiat.
I think some people do not like Crypto Currency because of its extreme volatility issues that are normal to Crypto Currencies, merchants and sellers do not want to accept a currency that could drop its value at any time and this is one of the reasons why some people don't like it. Seriously, Crypto Currencies are used as an asset and not a currency, you can definitely see it in the whole Crypto space.
Sure is a good combination,
For me I used my Crypto for saving and Fiat for paying,
I think it is a good way to save money.
It really depends on people on how will they use Crypto Currency or paper money and both of these valuable things are balanced in a way that most people don't see.