The economy is about distribution of stuff. Money is an abstraction; it's like points in a video game. We made it up. You're asking if one abstraction (ownership of a piece of a factory, land, or other business) ever needs to be converted into another (fiat money) to be worthwhile.
No. It doesn't.
I have a modest bit of savings. I hope to never spend it. I live frugally, since I see no upside to living lavishly. My savings means I can have the job I want. If my boss doesn't like what I do, they can fire me. If I lose my job, I'm not bankrupt, and have time to find another job. Money has less sway over me. Historically, that's actually been super-beneficial to my career, since I could focus on long-term things over short-term ones, and that's always eventually been recognized.
That only requires my wealth to be liquid if a situation comes up.
If I had more savings, I wouldn't need to work for anyone, though. I could do startups and things a lot ore freely. There would be no control over me. I'm pretty good at bootstrapping and operating in the black, but at this stage, the risk profile is too high for me to do this.
Moving up from there, if I had a trillion dollars in wealth, I'd live the same lifestyle, but my wealth would not only free me from control others have over me, but would allow me to control others. I could, for example, hire people to solve hunger, disease, education, or war.
At almost no point do I need actual fiat money.
There's an upside to having my wealth backed by factories, land, and other means of production. As a means of value-store, shares are in every way superior to fiat currency. Fiat currencies tend to inflate, while shares tend to grow in value because they're backed by something real.
Ultimately, there is no perfect value store. Nation-states also don't survive forever, and fiat currencies disappear too. There is value to a robust short-term (e.g. long enough to last my retirement) value store. I do understand that it's all zero sum, in the sense that if WWIII comes up, the zombie apocalypse, or rapture, neither shares nor money will have any meaning.
As a means of exchange, I agree fiat beats shares. I keep a small portion of my money in fiat, and a large portion in shares.
As a footnote, in the acquisition scenario, someone ultimately gets something they want. If I have a company with 1000 acres of land, five pieces of mining equipment, and so on, at the very end, it gets carved up into that stuff. That stuff has real, tangible value.