have it worse in first world countries than they did in France during the 1700s

In absolute terms? Definitely not. The lowliest "unskilled" worker today has vastly more amenities than even a 17th century nobleman could even dream of.

In relative terms, however? The ultra-rich robbed you, me and every single other person on this planet. And to this you may retort that you do not care about wealth and are content with what you have. I would applaud such an answer, but it would be besides the point. What we've been systematically robbed of, is our time. Years, decades that could be spent enjoying your lives with our loved ones, instead spent slaving away at a desk or in a factory only to make the few who have everything even more. That, to me, is absolutely unforgivable, especially since I've long since past my physical prime and am still being robbed of this time against my will.

Now, if you want to alter the claim to “the threat of violence is needed,” then I would be more inclined to agree; however, individually murdering certain billionaires is not productive;

Again, I disagree. There are about ~2700 billionaires on earth out of ~8 billion people. Killing half of them and having that wealth redistributed would solve more problems than it would create. But if I do that, I'm thinking like said billionaires.

Which is the only way to fight them. If you try the moral and legal route, you won't stand a chance because you'll be fighting within systems and rulesets they have created to give themselves every (unfair) benefit.

Sometimes the disgruntled worker who shanks the boss is the hero we need.