99% of people don't know what is centralized/decentralized, most of the times they make a terrible mistake thinking decentralized means the transaction is done by a 3rd part (ie. nodes in the network)
Decentralized / centralized can be defined (not limited) by:
1) Governance: Who controls it ?
2) Issuence and Distribution: Who creates & who sells it? mining? Someone create (from nothing
) and decide how much and when to "dump" it.
3) Custody: Where it is kept,
4) Audit system: How do you make sure the thing really works (Public / Private)
5) How transaction is processed: Self explained. Public Nodes / Private system.
To be decentralized all 5 items has to be achieved in such way (4,5 : Public)
Let's compare:
USD
1) US Central Bank (FED)
2) FED
3) Banks / FED
4) FED
5) Banks (Private)
Bitcoin/Ethereum/zcash/Monero/ etc:
1) Developers, Miners (If you don't like what is going on be free to fork it, the best idea wins)
2) Mining
3) You
4) It's all in the Blockchain
5) Miners/Segwit (all public nodes)
Ripple/Stellar/Iota/Neo:
1) Private Company / small group of people (damn that's a game over for me)
2) Private Company / small group of people (game over again)
3) You
4) Public Ledger? (someone confirm please!)
5) RippleNet (There are talks about they will open to public nodes)
The two more important items (1 and 2) to define a decentralized system is not achieved by Ripple, Stellar, IOTA and many others.
Honestly in my option all crypto that can't be mined then it will have a group of people who can manipulate it at any time, this include the PoS (rich gets rich theory)
Please let't me know what I'm missing.