On the other hand, anyone can invest in FAANG stocks and get a higher rate of return.
I think you have to take it on a case-by-case basis and you can't make a general claim. On balance, free markets have probably caused more cartel-like behavior in my industry but abandoning free markets would be strictly worse than the mix that we have now.
Left to themselves, corporations acquire monopolies. The market gravitates towards nasty local maxima when there is information asymmetry, or when people simply don't have enough spare resource to compare options properly (attention asymmetry?). The primary organised force against corporate opportunism is government.
Government does of course have its own failure modes, democracy regardless (for similar reasons) against which corporations and the free market operate.
Claiming that either half of the system is remotely capable of self-regulating is moronic.
Moving from feudalism to democracy clearly improved life for the average person, I'm not sure it's clear after that fact.
Exactly. And no civilization on earth has yet solved the "Power tends to corrupt; absolute power corrupts absolutely." problem at scale. In what society does power not exist in some form? In even the most primitive of human societies the first and best portion of the meal would be given to those who had the most political favor. We have control of a single vector in this equation, the size of the government. I see no other way.
You're not looking very hard. As I suggested above, we can pursue government policies (largely independent of government size) that favor decentralization. We don't have to throw up our hands in defeatism. We have perfectly good processes to implement these policies and improve our society. The only real obstacle, frankly, is the kind of fatalistic passivity you're proposing.
And just as there is no one major cause, there is no one major solution, like a wealth tax. Rather, we need to overhaul much of our financial and business regulation to favor decentralization. Limits on corporate and real estate ownership, corporate board participation, and business advertising would all go a long way toward reinvigorating small business and creating a healthier, less homogenized economy.