I understand what you're saying. Too few participants in the market with disproportionate leverage can sway the price of any asset countering the 'free market' ethos (look at silver).
I believe this is more of an issue for cryptos which are inflationary, where the coin supply is essentially never ending.
However on the other side of the (Bit)coin, I think currencies like Bitcoin have a trump card where deflation is built into the design. It's always going to get more scarce and more expensive as a result.
The closer it gets to its 21 million limit, the more expensive it will inevitably get.
If we have a situation where one or two players have so much more than anyone else then yes, they can influence the price and create fluctuations in the price but in terms of long term trend, I believe the price will tend to be going up and then stablise.
Let's say it's stabilised and a big market participant wants to disrupt by dumping a ton of bitcoins into the market ..this won't do anything but depress the price for a short time and as people realise the opportunity to buy bitcoin, it will rise and stablise again.
It'll be a self correcting mechanism.