i don't really know steem as a cryptocurrency or a blockchain, i think like most people i know it as a platform which looks a lot like reddit (steemit). and although it was advertised as decentralized platform for content creators and at first it looked that way but nothing about it is decentralized which is why i never liked it. i think it would have been a lot better if they found a way to make it really decentralized and p2p instead of a website like any others.
It's not just a cryptocurrency, it's a blockchain and steemit is just one of those applications built on it, we have a lot of them. 3speak for videos, dsound for audio, busy.org for articles and much more applications you can find them all here :
https://steemapps.com/About the decentralization, it is decentralized. We don't need any third party to transfer money. It's p2p without any fees and with 3 seconds speed of transaction. You can send any amount of money using steem. If you built something on steem, you will have the complete right to do what ever you want, you set your rules for your project and you're ready to go. I don't know where you see the centralization and how you can prove it.