So this theory tries to tell us that Bitcoin's price is a result of some sophisticated adoption curve, but from my point of view adoption is largely irrelevant for Bitcoin - most of those who own Bitcoin are speculators, some are short-term speculators, some are long-term speculators, but everyone is planning to at some point sell.
Adoption is important and speculators are not all in Bitcoin market. They are only one component in Bitcoin market and they have their roles, contributions, capital in the market but they are not all.
Adoption is important because it brings new people and new capital in the market. With time, bigger adoption, the market will have more people, from investors to speculators and traders, they all contribute to bigger trading volume in the market. With bigger trading volume, big investors have one more reason to join it because they will have less trouble to enter and exit the market with big capital.
Adoption is important for value of Bitcoin and because you said about speculators, they are contributing to price on the market in short term. Value is for long term and more sustainable grows with time.
So instead Bitcoin should be analyzed as a zero-sum investment game. If more money comes in than comes out, the price grows.
I agree about zero-sum game. It is true for traditional markets like stock market too.