while I agree that number of users is increasing exponentially (so far), the number of transactions is NOT, which was posted earlier.
Possible explanation-the absence of accurate statistics, but then the whole argument is mute.
If it is true the "
number of users is increasing exponentially (so far), the number of transactions is NOT" this would be congruent with my thesis that Bitcoin is abnormally skewed towards investors and not sufficiently balanced to (transaction) adopters.
Today it appears that a "concave down" [log-logistic] function would fit better than a straight line, but late last November people were arguing for a concave up (super exponential) model.
We have more history now so what we see now is more supported (by data) than what they saw historically. That doesn't necessarily make it more predictive, as it depends on our characterization of possible noise and other supporting logic for which model should be predictive.
IMO, the growth rate for bitcoin would need to decline strongly (or retreat over a long period) to truly invalidate the exponential growth model.
Your subjective bias is fooling you here. Mathematically false because there was never a mathematical confirmation that the
predictive model was correct in the first place. We are simply picking straws blindfolded unless we have historically complete examples and or some other well supported logic from which to argue which
predictive model should be correct.
Here's a model that fixes bitcoin's market cap at inception at $500,000. The "rationale" is that Satoshi spent approximately 2 years building it, and the market-value for Satoshi-level talent is $250,000 / year.

I argue this proposed model is invalidated because it is internally inconsistent. It is based on the notional of investment value of market cap as a starting point, yet you are modeling the Metcalf Law adoption value which is based not on investment adoption but rather on transaction adoption. In other words there is a category error here.
P.S. thanks so much for applying the effort for the examples and sharing. It really helps to discuss from your effort as I think it helps raise understanding.