the market cap is too small
as the market cap grows, it will take much more to move the price
That is not the only reason. Its market capitalization is more than $70 Bn. There are a lot of companies who aren't valued at those levels. Still Bitcoin is much more volatile.
Market cap doesn't even drive price. Market cap is a consequence of price.
Market cap is not a reason why the price fluctuates.I don't think Prince8 argued that market cap is driving the price. I think his point is that the larger the market, the more money it takes to move (or manipulate) the price in a meaningful way. Buying / Selling USD 1 million worth of BTC now has a lesser impact on the market than it would have 2 years ago.
Oh, yeah, that's a great point. I suppose that also means as Bitcoin becomes more widespread as an investment there is less money "on the sidelines" available to be invested AND each new dollar (as you say) doesn't have the same impact on price as the dollar before it did.