Nope. Not buyin' it. Many of the excesses of capitalism can be traced to indentured servitude prior to slavery and many more can be traced back to penal servitude prior to indentured servitude. The excesses of capitalism were imported directly from England, which wasn't a standout in Europe for feudal brutality by any measure.
More than that, we fought a war against slavery and it's not like things got better for everyone after the elimination of slavery, nor were things fine and dandy in the North where slavery was abolished. Most of the worst aspects of capitalism arose during the Gilded Age where wage slavery was an essential part of the economy and where industrialists thought it was fine and dandy to hire private armies like the Pinkertons to murder union sympathizers and organizers.
American capitalism is brutal because America, Britain and the other "neoliberal" countries of the world cast capitalism and socialism as Manichean absolutes whereas the rest of the world saw them as poles on a spectrum. Once the Tsar fell, the world spent a hundred years realigning itself on that spectrum. Those forces that were most directly oppositional to communism ended up with the most free-market excesses; those that were most directly oppositional to capitalism ended up with the most excesses of a command economy.
The non-aligned movement allowed nations that were not directly required to kowtow to one ideology or another to pick and choose the market characteristics that they wanted without adhering solely to one pole or the other. This is why countries like France have many free-market aspects and many socialist aspects. The effects are masked in other nations by graft, corruption and cronyism but by and large, the rest of the world uses socialist aspects where they make sense and capitalist aspects where they make money without crushing everyone. The problem is that cronyism destroys socialism eventually while it buttresses and strengthens capitalism.
American capitalism is brutal because for 60 years we were able to point at the Soviet Union and China and Cuba and Vietnam and Cambodia and Nicaragua and Venezuela and say "WE DON'T WANT THAT AND IF YOU DO YOU ARE THE ENEMY." Up until 2016, "socialist" was an epithet in American political discourse. Up until 1989, "socialist" was part of the title of our greatest enemy. Therefore, anything that sniffed of socialism was un-American by definition and anything capitalist was desirable.
Survival of the fittest, bitchez.