Well, don't you think if the whole world is dominated by cryptocurrency or bitcoin, then some people will face a huge problem?
I don't think so, Bitcoin as it is is just another mode of payment available to people just as PayPal,Cashapp, wise and the list is endless....so Bitcoin being the dominant coin would just limit peoples options.
I have discovered some of the reasons for this. For example-
1. When virtual currency or crypto-currency reigns all over the world, the banking system will be miserable, and a group of people (who do not know about crypto-currency or bitcoin) will be unemployed all over the world, who till now were working at the convenience of various banks.
Not sure which angle you looking at this from, but bitcoin alone can't solve employment issues as this is just a mode of payment or a store of value.
2: Unemployed people (due to a lack of knowledge of currency requirements or benefits) will not be able to handle this shock in the first place, due to which they will face various financial, lateral, physical, and mental problems, which is a big challenge for them.
Humans are naturally survivors, and if learning how to use cryptocurrencies makes this much easy, trust me they/we shall learn.
3: Many developing or underdeveloped countries (especially those with low leverage) will consider cryptocurrency a curse rather than a blessing due to their lack of proper understanding of its importance.
But as things stand, crypto is more widely used in developing countries as most try to use it for cheaper remittances, bypassing the tax channels and last keeping their wealth under the radar unlike developed countries where regulation follows every dime and people operate by the book .