I agree with you a lot here. But the possibility (fear) of the USD becoming worth next to nothing is not toooo far-fetched, and is part of what drives cryptocurrency adoption. Being able to afford 100 loaves of bread would be great, esp cpmpared to those with no btc, and if dollars are useless.
I agree that these numbers only work if one crypto - btc - is dominant. It's more likely that there will be a few, similar to how Visa, Master Card, Amex, Discover are now.