I have somewhat different idea than you! The first mistake you have made is to benchmark the definition of stable coin against the current set of definitions available. Stable coins in crypto space should have a different definition. The way bitcoin can't be bench-marked against the current definition of currency, similar way, crypto stable coins can't be bench-marked against the current definition of stable currency! That's wrong!!

Secondly, Stable coins are just a virtual representation of backed asset. If a stable coin is backed by USD, it can be called as USD future as per the current available definition, but not as per the crypto space where new sets of definitions are needed. It certainly is a economic property and not a technological one - Stablecoins represents the economic value only and not the technological aspect of it! So the argument is itself wrong! At least according to me!

I believe Stable coins are great for the crypto market because it provides convenience to the users. It surely looks like a future derivative of the backed asset, but it has many other utilities in the crypto space!