BCH, BTC, and Fair Market Value

Starting to see lots of information about BCH transaction rate going above BTC transaction rate and staying there. With lower fees and faster transactions, it makes a lot of sense.

What confuses me is why transaction rate is a factor of the coins Fair Market Value. This site tracks most coins and their fair value. BTC is clearly way over valued, but its value seems to be coming from its increasing rarity instead of its transactions quantity. BCH on the other hand is way undervalued even though its FMV is on a linear upward trajectory (thanks to increasing transaction rates). In fact, there doesn't seem to be any coin tracked there that is near its fair market value. So why/how do you see value in this metric and what are ways that could improve the FMV calculation? And, is FMV even a useful metric to research?