I disagree. Yes, the cryptocurrency is built for the banks and is pre-mined.
I will start by addressing the centralisation issue.
At present most Ripple validators are run by Ripple themselves. This is a strategic decision which has allowed them to secure and upgrade the network more easily in the early years of development. As time goes on more and more partners are running their own validators to decentralise the network. Notable examples include MIT:
https://ripple.com/insights/mitvalidator/
and more recently Gatehub.
You can expect to see more validators being run by trusted institutions in the coming years. So yes, Ripple is not fully decentralised yet, but it is moving in that direction. Compare this to Bitcoin in which most of the power is held by a handful of Chinese miners.
It is also worth remembering that Ripple's solution is primarily designed for banks, and banks may run into regulatory and security issues by moving their systems onto a fully decentralised network. Do regulations allow banks to have their transactions validated by anonymous and untrusted parties? I suspect banks are forming the Enterprise Ethereum Alliance for exactly this reason. Many Ethereum investors will applaud EEA whilst damning Ripple for not being fully decentralised.
Next the premine. Rather than adopting a wasteful proof of work system for securing the network, Ripple's consensus mechanism does not provide rewards to miners. Instead 80% of the initial 100bn XRP was allocated to Ripple (a massive source of funding) and 20% to the founders. There is no mining.
I believe the 20bn allocated to the founders was split like this:
9bn to Chris Larsen 9bn to Jed McCaleb 2bn to Arthur Britto
Chris Larsen has since donated 7bn to charity.
http://www.coindesk.com/ripple-price-rebound-ceo-7-billion-xrp-donation/
Jed McCaleb has left Ripple and set up a rival project, Stellar. After leaving Jed reached a settlement agreement with Ripple about the rate at which he would sell his remaining XRP, preventing any big dumps. Furthermore he agreed to donate 2bn of his holdings to charity:
https://forum.ripple.com/viewtopic.php?f=1&t=15885
As such, nearly half of the founders allocation has been pledged to charity and most of the rest is being sold under strict conditions.
The 80bn allocated to Ripple is sold and distributed by the company in a manner which allows them to encourage banks and gateways to adopt XRP and grow the network. You can read more about how Ripple uses its XRP to incentivise positive growth here:
https://ripple.com/xrp-portal/
So, Ripple is neither POW or POS, instead the majority of XRP was donated to the company (the premine) and serves as a pool of funds that is used to incentivise positive activity and grownthe network. This is a huge advantage.
Ripple understands that some investors are concerned about the fact that they hold so much XRP because they could theoretically dump a load of it crashing the price of XRP (in reality this would be suicidal and so they would never do it). As a result of this there has been talk of them using smart contracts to lock up some of their XRP holdings such that it can only be released according to pre-defined terms:
https://www.xrpchat.com/topic/3339-locking-up-ripples-xrp-with-crypto-conditions/
Ripple's XRP is primarily marketed at banks as a bridge currency for cross border transactions:
http://www.coindesk.com/ripple-banks-42-percent-international-payments/
They have a rapidly growing network. 15 of the top 50 banks currently work with Ripple.
We'll agree to disagree ;). You bring up valid facts, this was more of an editorial. As such, I remain astute in my belief.