What is somewhat interesting here on this thread and many other threads on this website is that FIRE is built upon ultimate faith in capitalism and the functioning of financial markets. In some ways FIRE foundationally preaches leaving behind some tenents of capitalism (you always need more, more, more, get out of the workplace that supports corporate profits, etc.) but yet relies on other tenents, namely corporate profits fueling an ever rising stock market.
I don't think this is an accurate representation of the FIRE concept. The FI goal is to save enough to be financially independent, typically through a combination of efficient spending and efficient investing and then if you want, RE is an option. It just so happens that investing in the stock market is
probably the fastest way to achieve that right now.
If investments and inflation were removed from the equation, lot's of people could still FIRE, it would just take longer. A 66% savings rate means 1 year of work pays for 3 years of expenses. Work from 20-45 and you should have enough to cover everything until you're 95. An oversimplified example, but my point is that it doesn't rely on the stock market.
I also don't think (reasonable) people pursuing FIRE have ultimate faith in financial markets. It's just a matter of making the best decision right now based on the available information. There's no such thing as a sure bet but betting on financial markets with money is a little bit like betting on the success of Chuck E. Cheese with their own tokens. I bet you all of my Chuck E. Cheese tokens that Chuck E. Cheese will stay open for 50 more years. Again, oversimplified, but something to think about.