That is probably approximately correct. However, there's a bit of a feedback loop there. The difficulty changes in response to the hash rate. And the hash rate

That is probably approximately correct. However, there's a bit of a feedback loop there. The difficulty changes in response to the hash rate. And the hash rate changes in response to the incentive to mine the coins. When the price goes up, the hash rate goes up, so the cost of mining goes up. So, while you are correct, the causality flows in both directions. It's really quite difficult to value any currency. Doubly so for a crypto currency.