So when are you going to sell your Bitcoin when it goes to $5K or more realistically less than $5K?
Bitcoin is slower than all this and violently fluctuates which loses people's money quickly. People also need to pay their bills in fiat anyway so whoever is receiving the Bitcoin needs to cash out to fiat anyway.
At that point you might as well just use fiat instead.
I did this dance at least 100 times and never ever had a problem with price fluctuation. Bitcoin is pretty stable on a 3-day timeframe.