it appears some of my assumptions were not correct. I assumed difficulty would be rising exponentially one way. Your graphs posted indicate that difficulty & price are directly linked, and are not linear or exponential, but rising & falling.
If I assume price is related to difficulty, why does difficulty rise & fall? The more I try to learn about BTC, the more complicated it is! I'm not trying to understand all of it, just enough to decide my own involvement! LOL
Price dictates difficulty. If existing miners (those who have the most accurate numbers to work with) can get more bitcoins by buying hardware then paying for them directly, they will buy hardware. If price drops below what it take to pay the electric bill, miners will turn off their hardware. There is often a time delay for bringing new hardware online though. Difficulty rises pretty quickly as existing hardware becomes profitable again, but it also overshoots as new hardware is purchased and isn't brought online until after the price corrects down.