I assumed all the rest are roughly the same idea.

My skepticism is about blockchain technology. It's the "currencies" I have doubts about.

My main idea is that the only way a cryptocurrency will have long-term value is if it becomes a default, dominant currency. By that, I mean at the same usage/confidence level as the dollar, pound, euro, etc.

The value of a currency is determined by supply and demand. Usually demand comes from usage. I.e. more people need euros to buy things. So that pushes the price of euros up.

If cryptocurrency stays in the world it's currently in, the trading world/ novelty purchase world, then it has no usage value. No demand -> price=0

The technical limits of bitcoin (energy usage, transaction speeds, transaction costs, limited supply, etc) make it even less likely to be a dominant currency, imo.
I don't know about the rest of them