That's a fair point actually, and one I can't answer, thank you for presenting that view point.

I would say this, hypothetically speaking...

XRP is a different creature to other cryptos for the fact that, right off the bat, a very large stake is owned by a company (effectively).
Your illustrative development of them owning various quantities is an an interesting one.
Perhaps the word 'centralised' is not correct...although the premise of it is, namely, that the direction of XRP can be influenced towards a certain direction if said holders wanted to because of their vast ownership of coins. By definition, this is not an organic development but a manufactured one, one primarily based on the commercial viability of the platform calculated and defined by a small group of individuals and therefore, 'centralised'.

However, this is my issue with crypto in the long run, it's ability to remain 'ethical'. Because although XRP has the dynamic of a lot of coins being owned by a relative few, the same can be true of other cryptos and their so called 'whales'. These creatures can also influence a coin one way or another, and have done so before, normally for no other reason than to create more money for themselves during a volatility created by them.

This is what I personally find interesting with this, my mind changing a little due to the very active discussion this post generated. Crypto is like the wild west at the moment! Will it be able to operate the way many envision it to, 'decentralised', either in name or action...or, would it become nothing more than a tool for the same institutions we have currently, albeit run with blockchain tech and clever math instead of a body?