What is wrong with this line of thinking:

Virtually all cryptocurrencies that are intended to be used as a replacement for fiat currency will become somewhat worthless.

All cryptocurrencies and their underlying technology are simply stage 1.

Stage 2 is where, once the technology has advanced enough from other peoples efforts, the Government creates its own either universal or country-based digital currency.

Afterwards, no one uses any other form of cryptocurrency (as a form of cash), except some of the techie-types or for purchases such on the dark web, because it is not the mainstream digital currency.

The government could also enact laws to prevent business from accepting any other form of digital currency, or make deals with payment processors to stop them from allowing other cryptocurrencies to be accepted.

Bitcoin may hold some value among collectors, as it was a first mover. Also, cryptocurrencies that are tied to a certain company or utility can hold value, such as how stocks function today.

But any fiat replacement coin besides the one adopted/created by government, ultimately will be worthless absent within some fringe communities.