Is the whole idea of proof of work or proof of stake quite unnecessary and superfluous for cyptocurrencies?
Can you elaborate some of your statements a bit?


  Now this time calculation is merely a matter of good faith, and hope that a majority abides by it.


When you have a look here you will see that the average block times is 9m 4s. Not too far away from the ten minutes the protocol tries to enforce.


  If you look a bit deeper, the whole hash function itself relies on good faith, also called the 51% risk/attack whatever.


Why does the hash function rely on good faith?

You're example ripple is in no means a replacement for bitcoin or ethereum. It is a completely centralised currency / system. We could use SWIFT banking instead.