Hash rate is also somewhat useless due to its fluctuating nature. While the fluctuation is lower for bigger coins, it can swing very wildly for smaller to medium coins.
And because of multipools the hashrate follows the current price very closely so if there's a price increase the hashrate follows.
So if we were to use hashrate as a metric similar to marketcap then a spike in hashrate/price would push the price/hashrate even higher becaue of newbies making irrational investments based on hashrate.
I agree that a single point-in-time snapshot may not be representative. If my suggestion from a few posts back of creating a graph were adopted then this variability would be visible.