If you search for it,
you'll realize that there isn't a standard definition for the “global adoption”. Bitcoiners tend to use it in their sentences as a way to describe Bitcoin's adoption by everyone on every part of the planet,
hence “global”.
The same people who believe in the so-called “global adoption” are the ones that see Bitcoin as a currency and believe in its “noble principles”. While I do get their enthusiasm, I think this is very much missing the point. Sad truth, but Bitcoin can't have a global adoption same like computers or internet had decades ago and I state this from an economic aspect. You should just think about it. The more users this thing has, the more the speculation. Not sure why it's being passed from forum members, but it does look like a pyramid scheme with utilities to me. Early adopters/investors get the chance to be included in the peak of the pyramid and earn more long-term. Overtime, I don't believe that it'll remain steady, it will probably reach millions of dollars.
What I want to mean in this topic is that the problem doesn't come from the fact that the majority sees it as an investment. The issue becomes clear if you notice its hierarchical structure. I'll quote myself to prevent re-writing a childish example:
(In the system below, 100 fresh bitcoins are brought into circulation every day.)
Let's assume that once upon a time, on an island, there were 100 people with 100 mushrooms in total and each one of them had 10 bitcoins, willing to use it as a currency. This means that each mushroom costs 10 BTC since there are 1000 BTC in total. But, hey, the next day, there are 1000 newcomers bringing 1000 mushrooms and they are also willing to use Bitcoin as a currency. But, unfortunately, there are only 1100 bitcoins in circulation which means that each mushroom now costs 1.1 BTC. Same thing would happen if that little community gained 10,000 new mushroom-farmers the next day. Every mushroom would cost 0.12 BTC.
Hierarchical structures don't stop global adoption of anything. There are 2,000ish billionaires in a world of 7,000,000,000 people. And this number is only getting more hierarchical thanks to the benefits that early adopters of pre-inflated cash get as cash gets inflated.
If anything, bitcoin has a better chance than other crypto with more concentrated distributions to become 'globally adopted'.
Bitcoin rises because of speculation, but the more speculation there is, the harder speculation becomes. It takes increasing amounts of cash to change its speculation. Speculation tends to stabilise, as people cash out when they have reached their 'moon' as you put it with your example. The person who was early loses power in such a system.
In your example, there are a limited number of people who can come to the island with their mushrooms, which should be devalued with infinite mushrooms using any currency anyways. That is supply and demand economics.