Bitcoin will never replace fiat cash. A coin everyone mints at the same rate will. It will also replace bitcoin and all of the shitcoins.
Mark my words.
Bitcoin runs off the fumes of fiat.
Sorry, but you are wrong with this stance because it was not the intention of Bitcoin creator to replace fiat money in the first place but instead, this will only serve as an alternative payment option at our choice.
Have we already heard that people are now 100% using Bitcoin? We don't coz it was not the reason for its existence and somehow, some people misunderstood for it. If we take a look around and even asking our friends, relatives, and our family members, they are not known to crypto, and probably they never know that Bitcoin can be used as a payment option online.