Stocks are nothing more than an investment tool. Bitcoin is a multifunctional tool, and is something that you don't necessarily need to convert to fiat in order to sustain yourself. If merchant adoption picks up in the forthcoming years, and that will very likely happen with LN, people are able to conveniently do grocery shopping, pay bills with Bitcoin, etc. The difference between Bitcoin as investment tool and a currency tool won't endlessly remain as massive as it might be right now. Stability, or something close to that will do miracles. It takes time, I know, but everything takes time in the end.
At some point there will be a time where you have to pay a nasty, like really nasty premium in order to convince people to sell their coins to you for fiat.
Indeed, there will come such a time. But until then Bitcoin is not strong enough. You are right in theory, but imho the reality is not like that, not yet.
"If merchant adoption picks up in the forthcoming years".. contains two big keywords: IF and YEARS. And you also admitted it takes time.
In that time is quite likely the world will face more than one crisis, and the first one will not be nice with us either.