I won't say I agree with the implication that the billionaires are the root of all evil (or the generalization in general, in modern day), but most importantly I think you're a well-read person who has core beliefs that drive this opinion, and our personalities and potentially worldviews are just different, hence this disagreement. I just blame the government first and foremost, rather than anyone using it for their benefit. This is literally the "agree-to-disagree" part, as far as I'm concerned.
As far as my personal beliefs, I've said it here quite a few times. I'm a libertarian essentially (with maybe some slight differences here and there on some issues, but at the core I'm basically a libertarian). I don't have a inherent hatred of billionaires or the rich, and especially not of capitalism. I believe capitalism has the potential to be great. What I'm saying doesn't stem from any kind of inherent dislike for most of the things involved in this subject matter. Really it's the opposite, I think people should be able to get rich if they provide value to society, they put in the work, and pay attention to market demands. I think it's perfectly fine for billionaires to exist, and there isn't anything inherently bad about it.
I don't think the billionaires are the root of all evil. But if you are blaming the system and not blaming the people that have shaped the system over the last 100+ years, it misses a core part of the problem. The laws, and power structure of our country didn't get this way on it's own. And it didn't just happen to work out in favor of what these companies want on accident. Billionaires have essentially been able to bribe, and buy out the government for quite a while now. The only way you can really put blame on the system without also putting blame on the people that are spending god knows how much to push the system in favor of what they want is to say the system was broken in the first place by allowing rich and influential people to buy out our public servants. Otherwise, it's billionaires that are shaping the system itself where they can to provide the results they would like to see for their bottom line.
I will expand on what I said about the system itself. It does need to be fixed, because if the ultrarich are able to pay to influence it this is going to continue, at the detriment of everyone else. I personally believe the only way to limit the scope of corruption is to limit the power the system itself is able to yield. The only fool proof way to stop it is to put limits on the scope of it's power, and on the people working in it. The avenues that are currently used to buy out people need to be completely closed. Corruption is going to happen in any system, especially one that is allowed to grant itself more power than it already held, and only fixing the problems it's caused without fixing the issue itself will just lead to the same thing happening again later down the line.
That said this didn't happen in a vacuum. And I think it's absolutely safe to put as much blame on the people that are willing to take advantage of it at the cost of everyone but them as I put on the failings of the system itself. Our congressmen are able to be bought and sold, the same thing for our presidents. The supreme court, idk I honestly haven't looked into the ways they are able to be influences so I won't say they are able to be bribed the same way, but i imagine it's probably at least somewhat similar. I would be surprised if there weren't people trying to lobby them some way or another.
I could pretty much write a never ending list of all the ways these things have been used at the detriment of the American people, but for the benefit of a small few. Louis Rossman's channel goes over some of them. And the things he covers do make a difference for normal people but what he covers is pretty limited in scope (right to repair, privacy, etc), there is SOOO many more examples of this kind of thing outside of that.