If any one crypto becomes too centralised, we can simply shift to others. Let them have BTC and XRP and whatever else they want, we can have BTG and Nano and VeChain or whatever.

I think that any coin that becomes a threat to it's investors will be instantly dumped for something better. Even before then, its price movement, or lack thereof, would probably cause a drop in popularity. Of course big money could manipulate prices, so keep an ear to the ground, watch the markets closely and diversify broadly.