Ripple is centralized.
No it's not. Their network is
decentralized. Sure they have pre-mine, but so do we.
Because Ripples exchange is distributed as opposed to centralized, the whole concept of co-location becomes fundamentally different. There is simply no central location near which you would co-locate for a speed advantage. Ripple exists on servers around the world, and anyone can easily spin up their own copy of a Ripple server for free. (The code is open source.)
https://ripple.com/blog/ripples-distributed-exchange-and-the-high-frequency-trading-arms-race/Emphasized important differences.