A system destined for growing centralisation can't be called decentralised. Where is the logic?
Your statement is at odds with itself:
1. By describing "A system destined for growing centralisation" you acknowledge that there many shades/degrees of centralization/decentralization.
2. By stating "...can't be called decentralised", you force a description of said shades/degrees into a binary TRUE/FALSE state.
That being said, I think the point you bring up about increasing centralization with network growth is a valid concern, and is a useful contribution to continuously-improving BitShares hivethink.