Let me put it in another way…
CoF p1 netts you 5g an hour.
How are you able to nett 5g an hour if you run around Orr to make it worth your time? Because earning anything less than 5g an hour, you might as well go back to CoF p1.
The answer is, the price of the loot you get increases to a point where they become worth 5g in total.
Which means that the price of the materials you get from Orr, has to rise to a point where it becomes equally rewarding as running CoF p1, not because ArenaNet made it to be so, but because of price increase.
When that happens, arbitrage is said to have taken place because that is the point where supply will come back and demand will normalize.
While I agree with your overall premise, I also think it’s more complex than that.
First, you can’t farm CoF solo. You can solo farm in Orr. This makes Orr more accessible.
Secondly, arbitrage only happens when there are two separate marketplaces. What you’re talking about is equilibrium prices, assuming that prices are set based on the value of the labor (in this case the opportunity costs of doing other things) it takes to produce a product. This was one of the biggest arguments in economics about 100 years ago, and demonstrably untrue. Just because something is expensive to make doesn’t mean it’s worth more money. What makes it worth more money is demand. Cost of labor provides a price floor, but since there’s no risk of going “out of business” in GW2 that price floor is not that strong.
Finally, farming CoF is only a viable alternative if you know about it and actually want to do that. Many players either do not know that it is more profitable to farm CoF, or do not know how much more profitable it is. Many other players (myself included) may just despise doing the dungeon and refuse no matter what.
So, it isn’t as simple as choosing between farming CoF and farming Orr. There are qualitative differences between these two methods of gaining wealth that make such a stark comparison misleading. This doesn’t even touch on the fact that CoF is largely a gold faucet, while Orr is largely a material faucet. Also I’m not discussing the messy relationship between price and demand, which is seldom linear or even knowable.
I do agree that, if ANet doesn’t do anything odd, that Crystalline Dust will probably increase more in price and probably stay there for quite some time. Demand for it is just too high for it not to. Think about it like this. If Crystalline Dust goes to 40s each someone will probably still buy it. If it goes to 50s, the same holds true. I’d imagine it could go as high as 99s and still sell (if slowly). That tells me that the market isn’t through shifting, and we’ll just have to wait for the prices to get high enough for people who have been hoarding the material to sell off their backstock.